Shares in fuel giant Caltex have tanked to a new four-year low after its Lytton refinery weighed heavily on a bleak earnings outlook.

Caltex stock fell by as much as 7.6 per cent to $25 in early trade on Tuesday after its unaudited profit guidance for the year ending 2018 showed replacement cost operating profit had dropped to between $533 million and $553 million, down by about 15 per cent at the mid point.

The company’s historic cost profit after tax is now $530 million to $550 million, a fall of about 13 per cent compared with 2017, while fuels and infrastructure earnings are set to decline 14 per cent from $666 million thanks to unplanned third-quarter outages at the Lytton refinery in Queensland, and a lower regional refining margin.

Shares in Caltex were still 6.54 per cent, or $1.77, lower at $25.28 at 1220 AEDT.

Meanwhile, chief executive Julian Segal said the company’s 2018 convenience retail earnings outlook of $295 million to $305 million is above the top end of the guidance range provided in October, assisted by crude and product prices falling in the fourth quarter.

In August, the company said it was considering selling part of its convenience retail assets valued at $2 billion, even as higher costs kept its first-half profit at the lower end of its guidance.