The director showed "If God Is Willing and Da Creek Don't Rise" at the National Association of Black Journalists convention in San Diego on Saturday. It airs in August on HBO.
When he was asked if BP cooperated he said, "Nobody was speaking to me from BP." A call to the BP press office wasn't immediately returned.
He also called on President Barack Obama to "bring the hammer" on BP and make the company pay.
BP PLC was leasing an oil rig that exploded on April 20, killing 11 workers and triggering the spill that has dumped 94 million to 184 million gallons of oil into the Gulf.