Oil prices fell on Thursday after a larger-than-expected build in US crude stockpiles stoked worries about slow demand, while signs that US interest rates could remain elevated added to pressure. Brent crude futures for April fell 43 cents, or 0.5%, to $83.25 a barrel by 0830 GMT, after rising 3 cents in the previous session. The April contract expires on Thursday and the more active May contract was down 33 cents at $81.82. US West Texas Intermediate crude futures were down 26 cents, or 0.3%, to $78.28 a barrel.