The deal between the two countries struck last month comes on top of the United States' regional arrangement for access to tuna via the vessel day scheme.
The Finance Minister Mark Brown said the US firms like the way the Cook Islands manages its fishery and it had established a reputation for being fair and reasonable.
"They want additional days from our surplus stock of vessel fishing days that we have available so we've managed to sell to the US fleets another hundred days of fishing access."
"I think they were looking to ensure that if they utilised all of the days that they'd been allocated under the regional programme, they just wanted an assurance that they had additional days up their sleeve if they wanted to use them," he said.
Photo: Cook Islands News Cook Islands finance Minister Mark Brown