The company, based at Newarthill, near Motherwell, saw its turnover rise 7.4% from £47.2m to £50.7m in 2012. That came in spite of European sales reversing from £27.7m to £14.6m, although UK turnover made up for the overseas slump by accelerating from £19.5m to £36.1m.
Accounts filed at Companies House show pre-tax profits soared from £3.05m to £4.8m across the 12 months.
Argent was bought by a subsidiary of London-based global conglomerate John Swire & Sons in July this year.
That was believed to have sparked multimillion-pound windfalls for managing director Jim Walker and other executives along with other shareholders including Sir Brian Souter's investment vehicle.
Argent said it had sold almost £5.1m of biofuel to Sir Brian's Stagecoach during 2012, up from £3.45m in 2011.
The accounts suggest Argent - which makes fuel from materials such as used cooking oil, fats and grease - was in healthy shape prior to the takeover deal by Swire.
The directors said the increase in profit exceeded expectations and added: "The market continued to be volatile throughout the year but management increased feedstock throughput, biodiesel output and improved operational performance such that a significant improvement in margins was achieved."
Cash had increased from £323,000 to almost £3.9m while net debt was shaved from £7.2m to less than £3.3m.
Directors' emoluments increased slightly from £578,000 to £587,000 however the highest paid saw their rewards slip from £305,000 to £276,000.
£1.1m of dividends were paid in 2012, compared to no payment in the prior year.
Average staff numbers were steady at 64 with employee costs at £2.6m.