Crude oil futures slipped in electronic trading Wednesday, as data showed a build in inventories and with investors looking ahead to the more closely watched U.S. supply report due later in the day.

New York Mercantile Exchange crude for September delivery CLU2 -0.28% shed 23 cents, or 0.3%, to $88.28 a barrel during Asian trading hours.

The losses wiped away most of Tuesday’s regular Nymex session’s slim gains, though Europe’s financial crisis had helped drive prices down 4% on Monday amid fears about future energy demand. Read more on Tuesday’s oil session.

Concerns that Greece may need to restructure its debt again shadowed markets Wednesday, hitting confidence as investors considered the impact of more fiscal drain on the regional economy.

On the supply front, the American Petroleum Institute reported late Tuesday a rise of 1.3 million barrels in crude inventories. Read more on API supply data.

The trade group also reported gasoline stockpiles up 2.3 million, and supplies of distillates up 2.6 million.

The numbers came ahead of the key weekly inventory report from the U.S. Energy Information Administration, with analysts polled by Platts expecting crude supplies to decline 250,000 barrels, the fourth decline in a row.

Gasoline stockpiles are seen down 750,000 barrels, and distillates inventories up 1 million barrels.

MarketWatch