In some areas the oil was knee-deep, fire department spokesman Jaime Moore said
A "handful" of businesses including a nightclub were affected.
The leak from a 20-inch pipe on West San Fernando Road was reported just after 1 a.m. local time. Four people at a medical business were evaluated with respiratorycomplaints, and two people were transferred to a hospital, Moore said.
The pipeline was shut off remotely and the spill was contained by fire officials, the department said.
A hazmat team was sent to the spill site.
Initial fire department reports indicated 1 million gallons spilled. The estimate was trimmed to 50,000 gallons a short time later, then trimmed again as cleanup progressed.
By dawn, an environmental cleaning company had vacuumed up most of the oil. Crews put down absorbent material to sop up the remaining crude and then used high-pressure hoses to wash the streets with a soap solution.
Fire department spokesman Erik Scott said there was no "visible evidence" that the oil entered storm drains, which empty into the Los Angeles River. But he said it's possible that some oil seeped under manhole covers.