A big surprise party was thrown by the U.S. Energy Department this morning when its weekly petroleum inventory report was released. Bears, rather than the bulls, did most of the celebrating, however.

Tomorrow, the Energy Information Administration, the statistical arm of the U.S. Energy Department, will release its much-watched weekly inventory report. Today, traders will jockey to square their books ahead of the report, guided by goings-on in the trading venues and the industry-supported American Petroleum Institute's inventory estimates.

Fundamentals are lining up for a continued pinch on oil refiners' margins. This morning's U.S. Energy Department inventory report showed a substantial drawdown in crude oil supplies and modest, though surprising, builds in refined products.

After Tuesday's losses in the U.S. crude oil market, bullish sentiment was bolstered by a key industry report about the supply of Texas Tea. Overnight trade in WTI crude was buoyed by the American Petroleum Institute's estimates that indicated crude inventories falling much more than analysts' expectations.

Crude oil futures tumbled in early trading today after government data showed surprising buildup in oil inventories.

Last week's Desktop piece, "Oil Fundamentals," illustrated the connection between contango in the West Texas Intermediate crude market and U.S. oil inventories. Contango, in case you missed the article, refers to successively higher premia built into the prices of futures reflecting the costs of carrying the commodity until delivery.

Sometimes readers wonder why so much attention is paid to the weekly oil inventory numbers published by the U.S. Energy Department's statistical service. Truth be told, a lot of trader breath is held awaiting each Wednesday morning release by the Energy Information Administration.

Whether you see BP's current performance as a potential buying opportunity or a sign of bleaker times to come, it pays to know how much influence its presence is having in your ETFs.

Oil gained modest ground in the overnight market in anticipation of this morning's holiday-delayed inventory report from the U.S. Energy Department. Prices for West Texas Intermediate crude futures rose 0.4 percent on Wednesday's NYMEX floor session.