diff --git a/contracts/Marketplace.sol b/contracts/Marketplace.sol
index f7a083a..6ea64b3 100644
--- a/contracts/Marketplace.sol
+++ b/contracts/Marketplace.sol
@@ -101,6 +101,10 @@ contract Marketplace is SlotReservations, Proofs, StateRetrieval, Endian {
       request.ask.maxSlotLoss <= request.ask.slots,
       "maxSlotLoss exceeds slots"
     );
+    require(
+      request.ask.expansion > 0 && request.ask.expansion <= 100,
+      "expansion must be [1, 100]"
+    );
 
     _requests[id] = request;
     _requestContexts[id].endsAt = block.timestamp + request.ask.duration;
diff --git a/contracts/Requests.sol b/contracts/Requests.sol
index 1771719..46be82b 100644
--- a/contracts/Requests.sol
+++ b/contracts/Requests.sol
@@ -20,6 +20,7 @@ struct Ask {
   uint256 reward; // amount of tokens paid per second per slot to hosts
   uint256 collateral; // amount of tokens required to be deposited by the hosts in order to fill the slot
   uint64 maxSlotLoss; // Max slots that can be lost without data considered to be lost
+  uint8 expansion; // Percentage of addresses eligible to reserve a slot halfway between request creation and when all network addresses are eligible to participate. [1-100].
 }
 
 struct Content {
diff --git a/test/Marketplace.test.js b/test/Marketplace.test.js
index 3b4f1a9..5911609 100644
--- a/test/Marketplace.test.js
+++ b/test/Marketplace.test.js
@@ -225,6 +225,18 @@ describe("Marketplace", function () {
       )
     })
 
+    it("is rejected when expansion is out of bounds", async function () {
+      request.ask.expansion = 0
+      await expect(marketplace.requestStorage(request)).to.be.revertedWith(
+        "expansion must be [1, 100]"
+      )
+
+      request.ask.expansion = 101
+      await expect(marketplace.requestStorage(request)).to.be.revertedWith(
+        "expansion must be [1, 100]"
+      )
+    })
+
     it("rejects resubmission of request", async function () {
       await token.approve(marketplace.address, price(request) * 2)
       await marketplace.requestStorage(request)
diff --git a/test/examples.js b/test/examples.js
index 06d8428..4f750a2 100644
--- a/test/examples.js
+++ b/test/examples.js
@@ -29,6 +29,7 @@ const exampleRequest = async () => {
       reward: 84,
       maxSlotLoss: 2,
       collateral: 200,
+      expansion: 60,
     },
     content: {
       cid: "zb2rhheVmk3bLks5MgzTqyznLu1zqGH5jrfTA1eAZXrjx7Vob",
diff --git a/test/ids.js b/test/ids.js
index 5ef1220..b1a3be3 100644
--- a/test/ids.js
+++ b/test/ids.js
@@ -2,7 +2,7 @@ const { ethers } = require("hardhat")
 const { keccak256, defaultAbiCoder } = ethers.utils
 
 function requestId(request) {
-  const Ask = "tuple(int64, uint256, uint256, uint256, uint256, uint256, int64)"
+  const Ask = "tuple(int64, uint256, uint256, uint256, uint256, uint256, uint64, uint8)"
   const Content = "tuple(string, bytes32)"
   const Request =
     "tuple(address, " + Ask + ", " + Content + ", uint256, bytes32)"
@@ -18,6 +18,7 @@ function askToArray(ask) {
     ask.reward,
     ask.collateral,
     ask.maxSlotLoss,
+    ask.expansion,
   ]
 }