diff --git a/package.json b/package.json
index 4a3c7f780241..3ba44a57c61f 100644
--- a/package.json
+++ b/package.json
@@ -18,6 +18,7 @@
     "lint:toc": "doctoc --title=\"**Table of Contents**\" ./specs ./meta"
   },
   "dependencies": {
-    "@eth-optimism/core-utils": "^0.8.1"
+    "@eth-optimism/core-utils": "^0.8.1",
+    "@ethersproject/constants": "^5.6.0"
   }
 }
diff --git a/packages/contracts/helpers/index.ts b/packages/contracts/helpers/index.ts
new file mode 100644
index 000000000000..639f068d0830
--- /dev/null
+++ b/packages/contracts/helpers/index.ts
@@ -0,0 +1,216 @@
+import * as RLP from '@ethersproject/rlp'
+import { BigNumber, BigNumberish } from '@ethersproject/bignumber'
+import { getAddress } from '@ethersproject/address'
+import {
+  hexConcat,
+  stripZeros,
+  zeroPad,
+  arrayify,
+  BytesLike,
+} from '@ethersproject/bytes'
+import { keccak256 } from '@ethersproject/keccak256'
+import { Zero } from '@ethersproject/constants'
+import { ContractReceipt, Event } from '@ethersproject/contracts'
+
+function formatNumber(value: BigNumberish, name: string): Uint8Array {
+  const result = stripZeros(BigNumber.from(value).toHexString())
+  if (result.length > 32) {
+    throw new Error(`invalid length for ${name}`)
+  }
+  return result
+}
+
+function handleNumber(value: string): BigNumber {
+  if (value === '0x') {
+    return Zero
+  }
+  return BigNumber.from(value)
+}
+
+function handleAddress(value: string): string {
+  if (value === '0x') {
+    // @ts-ignore
+    return null
+  }
+  return getAddress(value)
+}
+
+export enum SourceHashDomain {
+  UserDeposit = 0,
+  L1InfoDeposit = 1,
+}
+
+interface DepositTxOpts {
+  sourceHash?: string
+  from: string
+  to: string | null
+  mint: BigNumberish
+  value: BigNumberish
+  gas: BigNumberish
+  data: string
+  domain?: SourceHashDomain
+  l1BlockHash?: string
+  logIndex?: BigNumberish
+  sequenceNumber?: BigNumberish
+}
+
+interface DepostTxExtraOpts {
+  domain?: SourceHashDomain
+  l1BlockHash?: string
+  logIndex?: BigNumberish
+  sequenceNumber?: BigNumberish
+}
+
+export class DepositTx {
+  public type = '0x7E'
+  private _sourceHash?: string
+  public from: string
+  public to: string | null
+  public mint: BigNumberish
+  public value: BigNumberish
+  public gas: BigNumberish
+  public data: BigNumberish
+
+  public domain?: SourceHashDomain
+  public l1BlockHash?: string
+  public logIndex?: BigNumberish
+  public sequenceNumber?: BigNumberish
+
+  constructor(opts: Partial<DepositTxOpts> = {}) {
+    this._sourceHash = opts.sourceHash
+    this.from = opts.from!
+    this.to = opts.to!
+    this.mint = opts.mint!
+    this.value = opts.value!
+    this.gas = opts.gas!
+    this.data = opts.data!
+    this.domain = opts.domain
+    this.l1BlockHash = opts.l1BlockHash
+    this.logIndex = opts.logIndex
+    this.sequenceNumber = opts.sequenceNumber
+  }
+
+  hash() {
+    const encoded = this.encode()
+    return keccak256(encoded)
+  }
+
+  sourceHash() {
+    if (!this._sourceHash) {
+      let marker: string
+      switch (this.domain) {
+        case SourceHashDomain.UserDeposit:
+          marker = BigNumber.from(this.logIndex).toHexString()
+          break
+        case SourceHashDomain.L1InfoDeposit:
+          marker = BigNumber.from(this.sequenceNumber).toHexString()
+          break
+        default:
+          throw new Error(`Unknown domain: ${this.domain}`)
+      }
+
+      if (!this.l1BlockHash) {
+        throw new Error('Need l1BlockHash to compute sourceHash')
+      }
+
+      const l1BlockHash = this.l1BlockHash
+      const input = hexConcat([l1BlockHash, zeroPad(marker, 32)])
+      const depositIDHash = keccak256(input)
+      const domain = BigNumber.from(this.domain).toHexString()
+      const domainInput = hexConcat([zeroPad(domain, 32), depositIDHash])
+      this._sourceHash = keccak256(domainInput)
+    }
+    return this._sourceHash
+  }
+
+  encode() {
+    const fields: any = [
+      this.sourceHash() || '0x',
+      getAddress(this.from) || '0x',
+      this.to != null ? getAddress(this.to) : '0x',
+      formatNumber(this.mint || 0, 'mint'),
+      formatNumber(this.value || 0, 'value'),
+      formatNumber(this.gas || 0, 'gas'),
+      this.data || '0x',
+    ]
+
+    return hexConcat([this.type, RLP.encode(fields)])
+  }
+
+  decode(raw: BytesLike, extra: DepostTxExtraOpts = {}) {
+    const payload = arrayify(raw)
+    const transaction = RLP.decode(payload.slice(1))
+
+    this._sourceHash = transaction[0]
+    this.from = handleAddress(transaction[1])
+    this.to = handleAddress(transaction[2])
+    this.mint = handleNumber(transaction[3])
+    this.value = handleNumber(transaction[4])
+    this.gas = handleNumber(transaction[5])
+    this.data = transaction[6]
+
+    if ('l1BlockHash' in extra) {
+      this.l1BlockHash = extra.l1BlockHash
+    }
+    if ('domain' in extra) {
+      this.domain = extra.domain
+    }
+    if ('logIndex' in extra) {
+      this.logIndex = extra.logIndex
+    }
+    if ('sequenceNumber' in extra) {
+      this.sequenceNumber = extra.sequenceNumber
+    }
+    return this
+  }
+
+  static decode(raw: BytesLike, extra?: DepostTxExtraOpts): DepositTx {
+    return new this().decode(raw, extra)
+  }
+
+  fromL1Receipt(receipt: ContractReceipt, index: number): DepositTx {
+    if (!receipt.events) throw new Error('cannot parse receipt')
+    const event = receipt.events[index]
+    if (!event) {
+      throw new Error(`event index ${index} does not exist`)
+    }
+    return this.fromL1Event(event)
+  }
+
+  static fromL1Receipt(receipt: ContractReceipt, index: number): DepositTx {
+    return new this({}).fromL1Receipt(receipt, index)
+  }
+
+  fromL1Event(event: Event): DepositTx {
+    if (event.event !== 'TransactionDeposited')
+      throw new Error(`incorrect event type: ${event.event}`)
+    if (typeof event.args === 'undefined') throw new Error('no event args')
+    if (typeof event.args.from === 'undefined')
+      throw new Error('"from" undefined')
+    this.from = event.args.from
+    if (typeof event.args.isCreation === 'undefined')
+      throw new Error('"isCreation" undefined')
+    if (typeof event.args.to === 'undefined') throw new Error('"to" undefined')
+    this.to = event.args.isCreation ? null : event.args.to
+    if (typeof event.args.mint === 'undefined')
+      throw new Error('"mint" undefined')
+    this.mint = event.args.mint
+    if (typeof event.args.value === 'undefined')
+      throw new Error('"value" undefined')
+    this.value = event.args.value
+    if (typeof event.args.gasLimit === 'undefined')
+      throw new Error('"gasLimit" undefined')
+    this.gas = event.args.gasLimit
+    if (typeof event.args.data === 'undefined')
+      throw new Error('"data" undefined')
+    this.data = event.args.data
+    this.domain = SourceHashDomain.UserDeposit
+    this.l1BlockHash = event.blockHash
+    this.logIndex = event.logIndex
+    return this
+  }
+
+  static fromL1Event(event: Event): DepositTx {
+    return new this({}).fromL1Event(event)
+  }
+}
diff --git a/packages/contracts/package.json b/packages/contracts/package.json
index a74512a71bfb..39c775d64631 100644
--- a/packages/contracts/package.json
+++ b/packages/contracts/package.json
@@ -5,6 +5,11 @@
   "main": "index.js",
   "license": "MIT",
   "dependencies": {
+    "@ethersproject/address": "^5.6.0",
+    "@ethersproject/bignumber": "^5.6.0",
+    "@ethersproject/bytes": "^5.6.1",
+    "@ethersproject/keccak256": "^5.6.0",
+    "@ethersproject/rlp": "^5.6.0",
     "hardhat": "^2.7.1",
     "rlp": "^2.2.7"
   },
diff --git a/packages/contracts/tasks/deposits.ts b/packages/contracts/tasks/deposits.ts
index 7d194b685beb..eb7306a971b1 100644
--- a/packages/contracts/tasks/deposits.ts
+++ b/packages/contracts/tasks/deposits.ts
@@ -1,9 +1,15 @@
 import { task, types } from 'hardhat/config'
 import { Contract, providers, utils, Wallet } from 'ethers'
+import { Event } from '@ethersproject/contracts'
 import dotenv from 'dotenv'
+import { DepositTx, SourceHashDomain } from '../helpers/index'
 
 dotenv.config()
 
+async function sleep(ms: number) {
+  return new Promise((resolve) => setTimeout(resolve, ms))
+}
+
 task('deposit', 'Deposits funds onto L2.')
   .addParam(
     'l1ProviderUrl',
@@ -11,6 +17,12 @@ task('deposit', 'Deposits funds onto L2.')
     'http://localhost:8545',
     types.string
   )
+  .addParam(
+    'l2ProviderUrl',
+    'L2 provider URL.',
+    'http://localhost:9545',
+    types.string
+  )
   .addParam('to', 'Recipient address.', null, types.string)
   .addParam('amountEth', 'Amount in ETH to send.', null, types.string)
   .addOptionalParam(
@@ -26,11 +38,18 @@ task('deposit', 'Deposits funds onto L2.')
     types.string
   )
   .setAction(async (args) => {
-    const { l1ProviderUrl, to, amountEth, depositContractAddr, privateKey } =
-      args
+    const {
+      l1ProviderUrl,
+      l2ProviderUrl,
+      to,
+      amountEth,
+      depositContractAddr,
+      privateKey,
+    } = args
     const depositFeedArtifact = require('../artifacts/contracts/L1/DepositFeed.sol/DepositFeed.json')
 
     const l1Provider = new providers.JsonRpcProvider(l1ProviderUrl)
+    const l2Provider = new providers.JsonRpcProvider(l2ProviderUrl)
 
     let l1Wallet: Wallet | providers.JsonRpcSigner
     if (privateKey) {
@@ -52,7 +71,8 @@ task('deposit', 'Deposits funds onto L2.')
     ).connect(l1Wallet)
 
     const amountWei = utils.parseEther(amountEth)
-    console.log(`Depositing ${amountEth} ETH to ${to}...`)
+    const value = amountWei.add(utils.parseEther('0.01'))
+    console.log(`Depositing ${amountEth} ETH to ${to}`)
     // Below adds 0.01 ETH to account for gas.
     const tx = await depositFeed.depositTransaction(
       to,
@@ -60,11 +80,26 @@ task('deposit', 'Deposits funds onto L2.')
       '3000000',
       false,
       [],
-      {
-        value: amountWei.add(utils.parseEther('0.01')),
-      }
+      { value }
     )
     console.log(`Got TX hash ${tx.hash}. Waiting...`)
-    await tx.wait()
-    console.log('Done.')
+    const receipt = await tx.wait()
+
+    // find the transaction deposited event and derive
+    // the deposit transaction from it
+    const event = receipt.events.find(
+      (e: Event) => e.event === 'TransactionDeposited'
+    )
+    const l2tx = DepositTx.fromL1Event(event)
+    const hash = l2tx.hash()
+    console.log(`Waiting for L2 TX hash ${hash}`)
+
+    while (true) {
+      const tx = await l2Provider.send('eth_getTransactionByHash', [hash])
+      if (tx) {
+        console.log('Deposit success')
+        break
+      }
+      await sleep(500)
+    }
   })
diff --git a/packages/contracts/test/helpers.spec.ts b/packages/contracts/test/helpers.spec.ts
new file mode 100644
index 000000000000..a8e0f5f1a843
--- /dev/null
+++ b/packages/contracts/test/helpers.spec.ts
@@ -0,0 +1,54 @@
+import { expect } from 'chai'
+import { DepositTx, SourceHashDomain } from '../helpers'
+import { BigNumber } from '@ethersproject/bignumber'
+
+describe('Helpers', () => {
+  describe('DepositTx', () => {
+    it('should serialize/deserialize and hash', () => {
+      // constants serialized using optimistic-geth
+      // TODO(tynes): more tests
+      const hash =
+        '0xf5f97d03e8be48a4b20ed70c9d8b11f1c851bf949bf602b7580985705bb09077'
+      const raw =
+        '0x7ef862a077fc5994647d128a4d131d273a5e89e0306aac472494068a4f1fceab83dd073594de3829a23df1479438622a08a116e8eb3f620bb594b7e390864a90b7b923c9f9310c6f98aafe43f707880e043da617250000880de0b6b3a7640000832dc6c080'
+
+      const tx = new DepositTx({
+        from: '0xDe3829A23DF1479438622a08a116E8Eb3f620BB5',
+        gas: '0x2dc6c0',
+        data: '0x',
+        to: '0xB7e390864a90b7b923C9f9310C6F98aafE43F707',
+        value: '0xde0b6b3a7640000',
+        domain: SourceHashDomain.UserDeposit,
+        l1BlockHash:
+          '0xd1a498e053451fc90bd8a597051a1039010c8e55e2659b940d3070b326e4f4c5',
+        logIndex: 0,
+        mint: '0xe043da617250000',
+      })
+
+      const sourceHash = tx.sourceHash()
+      expect(sourceHash).to.deep.eq(
+        '0x77fc5994647d128a4d131d273a5e89e0306aac472494068a4f1fceab83dd0735'
+      )
+
+      const encoded = tx.encode()
+      expect(encoded).to.deep.eq(raw)
+      const hashed = tx.hash()
+      expect(hashed).to.deep.eq(hash)
+
+      const decoded = DepositTx.decode(raw, {
+        domain: SourceHashDomain.UserDeposit,
+        l1BlockHash: tx.l1BlockHash,
+        logIndex: tx.logIndex,
+      })
+      expect(decoded.from).to.deep.eq(tx.from)
+      expect(decoded.gas).to.deep.eq(BigNumber.from(tx.gas))
+      expect(decoded.data).to.deep.eq(tx.data)
+      expect(decoded.to).to.deep.eq(tx.to)
+      expect(decoded.value).to.deep.eq(BigNumber.from(tx.value))
+      expect(decoded.domain).to.deep.eq(SourceHashDomain.UserDeposit)
+      expect(decoded.l1BlockHash).to.deep.eq(tx.l1BlockHash)
+      expect(decoded.logIndex).to.deep.eq(tx.logIndex)
+      expect(decoded.mint).to.deep.eq(BigNumber.from(tx.mint))
+    })
+  })
+})
diff --git a/packages/contracts/yarn.lock b/packages/contracts/yarn.lock
index 416ab6d28565..0b8635d57e36 100644
--- a/packages/contracts/yarn.lock
+++ b/packages/contracts/yarn.lock
@@ -288,6 +288,17 @@
     "@ethersproject/logger" "^5.5.0"
     "@ethersproject/rlp" "^5.5.0"
 
+"@ethersproject/address@^5.6.0":
+  version "5.6.0"
+  resolved "https://registry.yarnpkg.com/@ethersproject/address/-/address-5.6.0.tgz#13c49836d73e7885fc148ad633afad729da25012"
+  integrity sha512-6nvhYXjbXsHPS+30sHZ+U4VMagFC/9zAk6Gd/h3S21YW4+yfb0WfRtaAIZ4kfM4rrVwqiy284LP0GtL5HXGLxQ==
+  dependencies:
+    "@ethersproject/bignumber" "^5.6.0"
+    "@ethersproject/bytes" "^5.6.0"
+    "@ethersproject/keccak256" "^5.6.0"
+    "@ethersproject/logger" "^5.6.0"
+    "@ethersproject/rlp" "^5.6.0"
+
 "@ethersproject/base64@5.5.0", "@ethersproject/base64@^5.5.0":
   version "5.5.0"
   resolved "https://registry.yarnpkg.com/@ethersproject/base64/-/base64-5.5.0.tgz#881e8544e47ed976930836986e5eb8fab259c090"
@@ -312,6 +323,15 @@
     "@ethersproject/logger" "^5.5.0"
     bn.js "^4.11.9"
 
+"@ethersproject/bignumber@^5.6.0":
+  version "5.6.0"
+  resolved "https://registry.yarnpkg.com/@ethersproject/bignumber/-/bignumber-5.6.0.tgz#116c81b075c57fa765a8f3822648cf718a8a0e26"
+  integrity sha512-VziMaXIUHQlHJmkv1dlcd6GY2PmT0khtAqaMctCIDogxkrarMzA9L94KN1NeXqqOfFD6r0sJT3vCTOFSmZ07DA==
+  dependencies:
+    "@ethersproject/bytes" "^5.6.0"
+    "@ethersproject/logger" "^5.6.0"
+    bn.js "^4.11.9"
+
 "@ethersproject/bytes@5.5.0", "@ethersproject/bytes@>=5.0.0-beta.129", "@ethersproject/bytes@^5.0.4", "@ethersproject/bytes@^5.5.0":
   version "5.5.0"
   resolved "https://registry.yarnpkg.com/@ethersproject/bytes/-/bytes-5.5.0.tgz#cb11c526de657e7b45d2e0f0246fb3b9d29a601c"
@@ -319,6 +339,13 @@
   dependencies:
     "@ethersproject/logger" "^5.5.0"
 
+"@ethersproject/bytes@^5.6.0", "@ethersproject/bytes@^5.6.1":
+  version "5.6.1"
+  resolved "https://registry.yarnpkg.com/@ethersproject/bytes/-/bytes-5.6.1.tgz#24f916e411f82a8a60412344bf4a813b917eefe7"
+  integrity sha512-NwQt7cKn5+ZE4uDn+X5RAXLp46E1chXoaMmrxAyA0rblpxz8t58lVkrHXoRIn0lz1joQElQ8410GqhTqMOwc6g==
+  dependencies:
+    "@ethersproject/logger" "^5.6.0"
+
 "@ethersproject/constants@5.5.0", "@ethersproject/constants@>=5.0.0-beta.128", "@ethersproject/constants@^5.0.4", "@ethersproject/constants@^5.5.0":
   version "5.5.0"
   resolved "https://registry.yarnpkg.com/@ethersproject/constants/-/constants-5.5.0.tgz#d2a2cd7d94bd1d58377d1d66c4f53c9be4d0a45e"
@@ -401,11 +428,24 @@
     "@ethersproject/bytes" "^5.5.0"
     js-sha3 "0.8.0"
 
+"@ethersproject/keccak256@^5.6.0":
+  version "5.6.0"
+  resolved "https://registry.yarnpkg.com/@ethersproject/keccak256/-/keccak256-5.6.0.tgz#fea4bb47dbf8f131c2e1774a1cecbfeb9d606459"
+  integrity sha512-tk56BJ96mdj/ksi7HWZVWGjCq0WVl/QvfhFQNeL8fxhBlGoP+L80uDCiQcpJPd+2XxkivS3lwRm3E0CXTfol0w==
+  dependencies:
+    "@ethersproject/bytes" "^5.6.0"
+    js-sha3 "0.8.0"
+
 "@ethersproject/logger@5.5.0", "@ethersproject/logger@>=5.0.0-beta.129", "@ethersproject/logger@^5.0.5", "@ethersproject/logger@^5.5.0":
   version "5.5.0"
   resolved "https://registry.yarnpkg.com/@ethersproject/logger/-/logger-5.5.0.tgz#0c2caebeff98e10aefa5aef27d7441c7fd18cf5d"
   integrity sha512-rIY/6WPm7T8n3qS2vuHTUBPdXHl+rGxWxW5okDfo9J4Z0+gRRZT0msvUdIJkE4/HS29GUMziwGaaKO2bWONBrg==
 
+"@ethersproject/logger@^5.6.0":
+  version "5.6.0"
+  resolved "https://registry.yarnpkg.com/@ethersproject/logger/-/logger-5.6.0.tgz#d7db1bfcc22fd2e4ab574cba0bb6ad779a9a3e7a"
+  integrity sha512-BiBWllUROH9w+P21RzoxJKzqoqpkyM1pRnEKG69bulE9TSQD8SAIvTQqIMZmmCO8pUNkgLP1wndX1gKghSpBmg==
+
 "@ethersproject/networks@5.5.1", "@ethersproject/networks@^5.5.0":
   version "5.5.1"
   resolved "https://registry.yarnpkg.com/@ethersproject/networks/-/networks-5.5.1.tgz#b7f7b9fb88dec1ea48f739b7fb9621311aa8ce6c"
@@ -469,6 +509,14 @@
     "@ethersproject/bytes" "^5.5.0"
     "@ethersproject/logger" "^5.5.0"
 
+"@ethersproject/rlp@^5.6.0":
+  version "5.6.0"
+  resolved "https://registry.yarnpkg.com/@ethersproject/rlp/-/rlp-5.6.0.tgz#55a7be01c6f5e64d6e6e7edb6061aa120962a717"
+  integrity sha512-dz9WR1xpcTL+9DtOT/aDO+YyxSSdO8YIS0jyZwHHSlAmnxA6cKU3TrTd4Xc/bHayctxTgGLYNuVVoiXE4tTq1g==
+  dependencies:
+    "@ethersproject/bytes" "^5.6.0"
+    "@ethersproject/logger" "^5.6.0"
+
 "@ethersproject/sha2@5.5.0", "@ethersproject/sha2@^5.5.0":
   version "5.5.0"
   resolved "https://registry.yarnpkg.com/@ethersproject/sha2/-/sha2-5.5.0.tgz#a40a054c61f98fd9eee99af2c3cc6ff57ec24db7"