The United States Treasury says Al-Qaeda is in its worst financial state for many years while the Taliban's funding is flourishing.
Assistant Secretary of State for terrorist financing David Cohen says al-Qaeda has made several appeals for funds already this year.
He says the influence of the network - which has been damaged by US efforts to choke funding - is waning.
However, the BBC reports the Taliban is considered in better financial shape, bolstered by Afghanistan's booming trade in drugs.
US Special Envoy to Afghanistan Richard Holbrooke has said the Taliban gets most of its funding from private benefactors in the Gulf and it's difficult to intercept and interrupt the flows of money.
Mr Cohen also noted a trend in terrorist organisations turning to criminal activities to finance themselves.
He said Hizbollah is involved in making and selling illegal copies of music and computer software, as well as cigarette smuggling.