Russian state oil firm Rosneft
Exxon CEO Rex Tillerson was expected to attend the event at Putin's Novo-Ogaryovo residence outside Moscow at 4 p.m. (1200 GMT), one of the sources told Reuters.
The landmark deal will grant Rosneft access to projects in North America, where Exxon is developing hard-to-recover reserves in West Texas, the Canadian province of Alberta and in the Gulf of Mexico, industry sources told Reuters last week.
The two companies will also seek to transfer know-how from those projects to develop Rosneft's own vast reserves of so-called 'tight' oil held in non-porous rock in Western Siberia.
Exxon, the largest listed oil firm in the world, struck an initial partnership with Rosneft last August to search for oil in three blocks of Russia's Arctic Kara Sea estimated to hold 36 billion barrels of oil.
Finalising that initial deal was contingent on Russia introducing an offshore tax regime that would make it economically viable for oil companies to shoulder the huge up-front costs of offshore exploration.
Putin said on Thursday he supported a reformed offshore tax regime that would eliminate export duties and cut rates of Mineral Extraction Tax, clearing the way for Monday's expected announcement.
The new regime will potentially provide the certainty needed to attract foreign investment into the Russian offshore, analysts at Bank of America Merrill Lynch, led by Karen Kostanian, wrote in a note on Monday.
We expect that multiple exploration joint ventures of Russian oil firms with foreign majors - similar to the one between Rosneft and Exxon - will follow, Kostanian added.
Rosneft shares rose 1.8 percent on Monday, outperforming a decline of 0.4 percent in the benchmark MICEX index <.MCX>.
CLOSING OUT THE DEAL
For Exxon, the deal secures access to Russia's offshore reserves, a prize that was coveted by British oil major BP
It also marks a turnaround in Russia for the U.S. oil major, which scaled back its involvement after its attempt to buy into Yukos - then the country's largest oil firm - was thwarted by the arrest in 2003 of Yukos owner Mikhail Khodorkovsky.
Khodorkovsky was later jailed for fraud and tax evasion, Yukos was bankrupted by back-tax claims and Rosneft snapped up its prime assets at auction to become Russia's largest oil firm.
The partners have announced that they will invest $3.2 billion in exploring for oil in the Arctic and the Black Sea, but eventual investments could run into the tens, or even hundreds of billions of dollars, insiders say.
Russia, the world's largest oil producer, needs to develop its offshore energy riches to meet its long-term goal of sustaining output at above 10 million barrels per day as flows from its oil-producing heartland of Western Siberia slow.
Analysts caution, however, that commercial offshore production is years - and possibly decades - away and say that applying to Russia the modern recovery methods that have boosted U.S. oil production of late could prove to be a quicker win.
Rosneft has said that it has an estimated 2.5 billion tonnes of tight oil in the so-called Bazhenov formation - a deposit discovered by Soviet-era geologists who were unable to develop a viable approach to extracting its reserves.
The Exxon-Rosneft deal marks a personal milestone for Igor Sechin, Russia's deputy premier and energy 'tsar', as Putin - elected as president last month - prepares to form a new administration.
The next government will be headed by outgoing President Dmitry Medvedev in a job switch with his mentor Putin. Medvedev has a history of conflict with Sechin, whom he ousted as Rosneft's chairman last year.
Sechin, who has been close to Putin for two decades, could cement his bid to stay on with the Exxon-Rosneft deal, although a move to one of the security structures that report directly to the Kremlin has also been mooted.
(Additional reporting by Gleb Bryanski; Writing by Douglas Busvine; editing by Elizabeth Piper)