Oil prices have risen 75% in about three months or less since hitting 12-year lows of around $27 a barrel for Brent in late January and about $26 for US crude in mid-February.
For April, the two benchmarks are up nearly 20% for their largest monthly gain in a year.
The rally, partly driven by the 6% drop in the dollar this year, has persisted despite US crude stockpiles growing to all-time highs above 540mn barrels, according to government data on Wednesday.
Brent futures were up 36 cents at $47.54 a barrel by 10:49 am, after setting a year-to-date high at $47.73.
US crude's West Texas Intermediate (WTI) futures rose 15 cents to $45.48, after hitting a 2016 high at $45.71.
"The market seems 'invincible,' and well supported my money flow," said Scott Shelton, broker at ICAP in Durham, North Carolina.
The dollar fell half a%, sliding for a fourth day in a row and to a two-week low against a basket of currencies. Declines in the dollar tend to make commodities denominated in the greenback, including oil, more attractive to holders of the euro and other currencies.
Many analysts believe the global glut in oil will ease from the second half of the year into mid-2017.
"The perception view crowd are starting to call the oil market rally the beginning of what will be a long bull market," said Dominick Chirichella, senior partner at the Energy Management Institute in New York.
"Clearly, the market is primarily focused on the forward supply-and-demand picture while continuing to push the bearish nearby fundamentals further into the background," he said.
While US oil production itself has fallen, imports of crude into the country have risen and a global oversupply looks set to grow as major exporters from Saudi Arabia to Russia and Iran ramp up output in a battle for market share.
Even so, analysts said oil near or above $50 a barrel could make drilling attractive again for US shale producers, potentially creating unmanageable supplies that sparked the collapse from the $100 levels of mid-2014.
"Some producers are also likely to use the higher price level for hedging transactions, which would likewise prevent any future fall in production," Commerzbank said.
