The Asia Times notes:
Relief organizations have calculated that as much as 75% of foreign aid is directly tied to trade access or other economic and political strategies. Some comes with so many strings attached, including preferential tendering on contracts and the hiring of consultants, that only 30-40% of dollar value is ever realized. US policy dictates that much foreign aid be spent on costly imported medicines, weapons, agricultural produce or manufactured goods. Some European nations have a similar approach.