Oil prices fell after a massive earthquake shook Japan, the world's third-largest oil consumer, sending a tsunami sweeping across the Pacific Ocean and pushing US crude prices below $100.

As the implications for oil demand in the region affected by the earthquake received attention, investors also monitored a planned day of demonstrations in top oil exporter Saudi Arabia and the violence in Libya, where oil exports have been disrupted.

Brent crude futures for April delivery fell $1.16 to $114.27 a barrel having fallen as low as $112.25.

US crude futures for April delivery fell $1.80 to $100.90 a barrel, having briefly traded at $99.01.

With the earthquake shutting some refineries in Japan, refiner profit margins for gasoline in the United States jumped to $24.96 from $22.76 on Thursday.

The heating oil crack spread rose to $26.43 a barrel from $25.18 on Thursday.

Brent's premium to the US benchmark West Texas Intermediate crude rose 63 cents to $13.18 a barrel, after falling below $8 this week and reaching a record above $17 last week.

Japan was hit by a magnitude 8.9 earthquake, the largest since observations began in the late 19th century.

While the full extend of damage was still being assessed, analysts said the images and reports so far did not suggest a major economic and financial disaster.

'Crude oil futures have fallen sharply as a sizable portion of Japan's oil refinery capacity has been shut due to the earthquake and tsunami. Data from China showing higher inflation also added pressure,' said Joe Posillico, broker at MF Global in New York.