Contracts of Affreightment (COA) are used when a shipowner or ship operator agrees to transport a given quantity over a fixed period of time. Unlike other charterparties, no specific ship is named in the charterparty. It is up to the shipowner or ship operator to provide ships as needed for the project. In tanker chartering, due to the sensitivity of port states regarding oil pollution, it is likely that the Contracts of Affreightment (COA) will include specific requirements regarding the ships employed which would probably extend to the shipowner having to provide the charterer with a list of ships likely to be employed in the contract. Contracts of Affreightment (COA) gives the shipowner considerable freedom to manage the fleet to the best advantage. Furthermore, shipowner or ship operator charter in ships if his own fleet is engaged in more profitable employment elsewhere. Contracts of Affreightment (COA) is common with owners of small coasters employed in short voyages, as it saves having to charter a ship for each movement. Contracts of Affreightment (COA) is also used by government charterers for international trades.
There are several standard charter parties for Contracts of Affreightment (COA) such as Volcoa and Intercoa. Standard charterparty forms are designed to be used in conjunction with voyage charter forms for each voyage which is undertaken under the Contracts of Affreightment (COA).