Index: binaries/data/mods/public/gui/session/menu.js
===================================================================
--- binaries/data/mods/public/gui/session/menu.js
+++ binaries/data/mods/public/gui/session/menu.js
@@ -31,7 +31,7 @@
 /**
  * Quantity of goods to sell per click.
  */
-const g_BarterResourceSellQuantity = 100;
+const g_BarterResourceSellQuantity = 1;
 
 /**
  * Multiplier to be applied when holding the massbarter hotkey.
Index: binaries/data/mods/public/simulation/components/Barter.js
===================================================================
--- binaries/data/mods/public/simulation/components/Barter.js
+++ binaries/data/mods/public/simulation/components/Barter.js
@@ -94,7 +94,6 @@
 	{
 		var amountToAdd = Math.round(prices["sell"][resourceToSell] / prices["buy"][resourceToBuy] * amount);
 		cmpPlayer.AddResource(resourceToBuy, amountToAdd);
-		var numberOfDeals = Math.round(amount / 100);
 
 		// Display chat message to observers
 		var cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
@@ -116,11 +115,12 @@
 		}
 
 		// Increase price difference for both exchange resources.
-		// Overal price difference (constant + dynamic) can't exceed +-99%
+		// Overall price difference (constant + dynamic) can't exceed +-99%
 		// so both buy/sell prices limited to [1%; 199%] interval.
-		this.priceDifferences[resourceToSell] -= this.DIFFERENCE_PER_DEAL * numberOfDeals;
+		var difference = this.DIFFERENCE_PER_DEAL * Math.ceil(amount / 100)
+		this.priceDifferences[resourceToSell] -= difference;
 		this.priceDifferences[resourceToSell] = Math.min(99 - this.CONSTANT_DIFFERENCE, Math.max(this.CONSTANT_DIFFERENCE - 99, this.priceDifferences[resourceToSell]));
-		this.priceDifferences[resourceToBuy] += this.DIFFERENCE_PER_DEAL * numberOfDeals;
+		this.priceDifferences[resourceToBuy] += difference;
 		this.priceDifferences[resourceToBuy] = Math.min(99 - this.CONSTANT_DIFFERENCE, Math.max(this.CONSTANT_DIFFERENCE - 99, this.priceDifferences[resourceToBuy]));
 	}
 
Index: binaries/data/mods/public/simulation/components/tests/test_Barter.js
===================================================================
--- binaries/data/mods/public/simulation/components/tests/test_Barter.js
+++ binaries/data/mods/public/simulation/components/tests/test_Barter.js
@@ -82,7 +82,7 @@
 TS_ASSERT(cmpBarter.PlayerHasMarket(11));
 
 // ExchangeResources
-// Price differences magnitude are caped by 99 - CONSTANT_DIFFERENCE.
+// Price differences magnitude are capped by 99 - CONSTANT_DIFFERENCE.
 // If we have a bigger DIFFERENCE_PER_DEAL than 99 - CONSTANT_DIFFERENCE at each deal we reach the cap.
 TS_ASSERT(cmpBarter.DIFFERENCE_PER_DEAL < 99 - cmpBarter.CONSTANT_DIFFERENCE);
 
@@ -94,12 +94,12 @@
 TS_ASSERT_EQUALS(sold, 100);
 TS_ASSERT_EQUALS(bought, Math.round(100 * (100 - cmpBarter.CONSTANT_DIFFERENCE + 0) / (100 + cmpBarter.CONSTANT_DIFFERENCE + 0)));
 
-// With an amount which is not a multiple of 100, price differences are not updated. That sounds wrong.
+// If the amount is not a multiple of 100.
 cmpBarter.priceDifferences = { "wood": 0, "stone": 0, "metal": 0 };
 cmpBarter.ExchangeResources(11, "wood", "stone", 40);
 TS_ASSERT_EQUALS(cmpBarter.restoreTimer, 7);
 TS_ASSERT(timerActivated);
-TS_ASSERT_UNEVAL_EQUALS(cmpBarter.priceDifferences, { "wood": 0, "stone": 0, "metal": 0 });
+TS_ASSERT_UNEVAL_EQUALS(cmpBarter.priceDifferences, { "wood": -cmpBarter.DIFFERENCE_PER_DEAL, "stone": cmpBarter.DIFFERENCE_PER_DEAL, "metal": 0 });
 TS_ASSERT_EQUALS(sold, 40);
 TS_ASSERT_EQUALS(bought, Math.round(40 * (100 - cmpBarter.CONSTANT_DIFFERENCE + 0) / (100 + cmpBarter.CONSTANT_DIFFERENCE + 0)));