European oil and gas majors have doubled their planned spending on low-carbon energy in just two years, from 10% of their 2019 capex to 25% of their total current spending plans, Wood Mackenzie said on Thursday.

In 2019, European oil majors aim to invest an average of $2 billion a year in alternative energy, accounting for 10 percent of capex. By 2021, the companies aim to invest an average of $4 billion a year in clean energy, or an average of 25 percent of capital expenditure.

Tom Ellacott and Greig Aitken of WoodMac's enterprise research team said Spain's Repsol had the most aggressive investment targets in low-carbon energy, accounting for 35 percent of its total annual spending.

Experts at WoodMac said most European giants are targeting renewable energy, especially solar and onshore and offshore wind, as these technologies are already commercialised and scalable, giving big oil companies access to the low-carbon energy they seek.

In addition to doubling investment in clean energy, WoodMac noted that the main difference from 2019 is that U.S. supergiants ExxonMobil and Chevron have also committed to investing in low-carbon energy.

American giants are betting on renewable fuels and carbon capture and storage (CCS) projects, but they are steering clear of solar and wind power.

In Europe, bp, Shell, Eni, Equinor and Total Energy have ramped up investment in renewable power generation, electric vehicle charging networks, hydrogen and CCS. In the offshore wind sector, oil and gas majors say they have the ability and skills to develop offshore wind power.