Indonesia's Cilacap oil refinery and Cepu oilfield in East and Central Java are running normally, officials said, despite volcanic ash fallout from the eruption of Mount Kelud.
Mount Kelud erupted on Thursday night, sending a plume of ash and sand 17 kilometres (10 miles) into the air and forcing the closure of five airports in the densely populated region.
The volcano is 90 km south of Indonesia's second biggest city Surabaya, a major industrial centre.
Cilacap, about 360 km west of Mount Kelud, is home to Indonesia's largest refinery, operated by state oil and gas company Pertamina. The plant's 348,000-barrels-per-day (bpd) capacity makes up about a third of Indonesia's total.
"Cilacap operations are normal, although ash has indeed reached the Cilacap area. As a preventative measure, we have immediately prepared air filters for equipment there," Pertamina spokesman Ali Mundakir told Reuters by text message.
Separately a spokesman for Exxon Mobil Corp said ash from Mount Kelud had reached the company's crude production facility in Cepu, but that operations had not been disrupted.
The Cepu exploration block is about 120 km from Kelud. The block's Banyu Urip oilfield, Indonesia's biggest crude find in three decades, was producing around 26,000 bpd as of April 2013.
A drilling programme launched last year is aimed at increasing the field's output to 110,000 bpd by mid-year.