Jame's Bradley's The China Mirage is a pretty good book on this. FDR didn't want to get into a war with Japan, and in his oil embargoes/financial asset freezes

Jame's Bradley's The China Mirage is a pretty good book on this. FDR didn't want to get into a war with Japan, and in his oil embargoes/financial asset freezes he left loopholes that would allow Japan to continue buying oil while convincing his political base that he was being tough on Japan. The bill was drafted in a way where Japan could submit requests to the state department and treasury to unfreeze enough assets to continue buying oil. However, FDR's assistant secretary of state, Dean Acheson, took a harder line on Japan and when FDR was meeting with Churchill in Newfoundland in August 1941 and Japanese tankers arrived for their preapproved oil shipments, Acheson refused to unfreeze Japanese funds so they could buy the oil and turned FDR's bill into an actual embargo.