U.S. agricultural processor Archer Daniels Midland Co posted higher third-quarter earnings on Tuesday amid improved oilseed processing and ethanol margins and rising demand for grains.

For the fiscal third quarter ended March 31, ADM reported net earnings of $421 million, or 65 cents a share, compared with $3 million, or nil per share, a year earlier.

Excluding costs for buying back debt, ADM posted earnings of 72 cents per share, matching the average analyst estimate, according to Thomson Reuters I/B/E/S.

Third quarter revenue rose to $15.145 billion, compared with $14.842 billion a year earlier.

Archer Daniels Midland of Decatur, Illinois, is one of the largest U.S. processors of corn and soybeans and a top U.S. ethanol producer.

Its corn processing segment profit increased to $104 million, up from $49 million the prior year, as bioproducts results rebounded from a loss last year amid lower average corn prices and improved ethanol margins.

But sweeteners and starches profit dropped from a year earlier on lower average selling prices.

Operating profit in ADM's oilseeds processing segment rose to $405 million, up 81 percent from the same period a year earlier, as last year's drought-reduced South American soybean crop boosted margins and volumes at ADM's North American facilities.

Strong oilseed demand in Asia and improved demand for vegetable oil-based biodiesel in Europe and South America further bolstered profit in the segment.

Agricultural services segment profit increased to $165 million, up $44 million from a year ago, on abundant global grain supplies and steadily rising demand.

ADM's other business segments, which include wheat and cocoa processing, posted net earnings of $22 million, compared with a loss of $140 million a year earlier.

Shares of ADM were down 17 cents to $27.55 in premarket trading.

(Reporting by Karl Plume, editing by Gerald E. McCormick and Derek Caney)