Russia's oil and gas revenue in October is set to jump to 1.17 trillion roubles ($12.16 billion), up 52% from September thanks to the once-a-quarter payment of oil profit-based tax, Reuters calculations showed on Tuesday.

At the same time, the revenue is likely to have declined this month by 28% from October 2023 because oil prices fell, the rouble strengthened and so-called damper subsidies to refineries were nullified a year ago due to high fuel prices.

Oil and gas revenue has been the most important source of cash for the Kremlin, accounting for about a third to a half of total federal budget proceeds over the past decade.

According to Reuters calculations, the oil profit-based tax payments will reach 435 billion roubles this month.

In total, oil and gas revenue for January - October are set to rise by 32% year on year to 9.5 trillion roubles.

For 2024 as a whole, the government budgeted for federal revenue of 10.7 trillion roubles from oil and gas sales, up 21% from 2023, when weaker oil prices and a fall in gas exports reduced the revenue by 24%.

That 2024 target was revised down from initial plans for 11.5 trillion roubles.

Russia has heavily increased defence and security spending since launching its invasion of Ukraine, what it calls its special military operation, in February 2022, leading to two consecutive annual deficits exceeding 3 trillion roubles, about 2% of GDP.

($1 = 96.2500 roubles)

(Reporting by Reuters; Editing by Elaine Hardcastle)