* Share buyback starts immediately
* Latest European oil firm to do so
* Johan Sverdrup oilfield starts production
* Last of the giant North Sea fields
* Shares up 6.5%, best performer of European oil stocks (Adds CFO, share, context, bullet points)
By Nerijus Adomaitis and Terje Solsvik
OSLO, Sept 5 (Reuters) - Equinor on Thursday launched a $5 billion share buyback and said its Johan Sverdrup oilfield, the largest North Sea discovery in more than three decades, will come on stream in October, a month earlier than planned, lifting its shares.
Equinor is the latest European oil firm to launch buybacks, after BP Shell and Total. It will be completed by end-2022, with the first tranche of $1.5 billion starting immediately and ending no later than Feb. 25, 2020.
The Norwegian state will maintain its 67% share in the firm.
"We have over the last years built a strong financial position with solid credit ratings and a net debt ratio around 20%," Equinor Chief Executive Eldar Saetre said in a statement.
Shares in Equinor were up 6.5% at 0716 GMT, the best performers in the European STOXX oil and gas index, up 1.06%.
"The upcoming start-up of the world-class Johan Sverdrup field, combined with several other new fields in production, provides additional confidence in our outlook for production growth and increased cash generation capacity," said Saetre.
LAST OF THE GIANTS
Discovered in 2010, Sverdrup may be the last of the giant North Sea oilfields. Nothing of that size has been found since, and it is Norway's biggest industrial development by far. There are no other field developments of that size planned in the coming years.
Its start-up will significantly boost the North Sea region's crude oil shipments and the cash flow of the field's owners.
Trading sources last Friday told Reuters that Equinor had listed 11 possible Sverdrup oil cargoes for October shipment, but the company said at the time that a November start was still its primary target.
The field's first phase is projected to reach a peak output of 440,000 barrels per day of oil in summer 2020.
The second phase of Sverdrup is expected to come on stream in late 2022, after which output could reach 660,000 barrels per day, Equinor added.
In addition to Equinor, Aker BP, Lundin Petroleum, Total and Norwegian state firm Petoro are licence holders in Sverdrup.
Alongside the share buyback, Equinor will continue to grow its dividends, keep investing in new assets and maintain its net debt ratio in a range of 15-30%, Chief Financial Officer Lars Christian Bacher told Reuters.
For now, Equinor was keeping its full year 2019 production guidance unchanged. It is expected to be at similar levels as in 2018, while capital spending is still seen at $10-11 billion, he said.
Asked whether Sverdrup could be the last of the big discoveries off Norway, Bacher said: "I hope not." (Writing by Gwladys Fouche; Editing by Stephen Coates/Sherry Jacob-Phillips/Jane Merriman)