A US energy department report to be released later in the day is expected to show another rise in US commercial crude stockpiles, indicating softer demand in the world's top oil consumer.
At around 0910 IST today, US benchmark West Texas Intermediate (WTI) for May delivery was up 30 cents, or 0.78 per cent, at USD 38.58 and Brent crude for May was 18 cents, or 0.46 per cent, higher at USD 39.32.
The dollar weakened after Yellen said yesterday that interest rates were not likely to rise before June and that any move will be slow and gradual.
A weaker US currency makes dollar-priced oil cheaper for holders of other units, encouraging traders to buy and lifting prices.
Also Read
But analysts said any oil price rise not driven by real demand is unlikely to last.
"The oil price advance today is going to be quite limited. If it hinges on US dollar weakness, it is not going to go much higher," said Bernard Aw, market strategist at IG Markets in Singapore.
Prices have collapsed from levels above USD 100 in mid-2014 largely due to supply outrunning demand as global economies, particularly China, suffer a growth slowdown.
Major producers led by Russia and Saudi Arabia will meet in Doha on April 17 to discuss measures to stabilise prices, including a proposal to freeze output.