The leaders of the world's largest energy exporters discussed an extension of an Opec agreement to cap oil output and oversaw the signing of deals which officials said were worth billions of dollars.
While last month's rally sent oil into a bull market amid stronger demand prospects, prices have struggled to hold above $52 a barrel on concern rising US output may offset OPEC-led supply cuts.
OPEC and its partners, including Russian Federation, need to extend their oil-production cuts for at least three more months to keep crude prices at current levels, according to UBS Group AG.
Oil prices rose on Thursday on signs that Saudi Arabia and Russian Federation would limit production throughout next year outweighed record USA exports and the return of production at a major Libyan oil field.
Under the agreements, Saudi Arabia is set to buy S-400 air defence systems, Kornet anti-tank guided missile systems and multiple rocket launchers.
The message of further joint Saudi-Russia action on output helped push up oil prices on Thursday. The group's current agreement expires at the end of next March, and as yet there's no decision on extending or deepening the cuts. The Saudi king will stay in Moscow till October 7.
The expert called attention to the fact that Moscow and Riyadh's cooperation in business and energy trade has already borne fruit.
Iran and Saudi Arabia have supported opposing sides in ongoing conflicts in Syria and Yemen.
"Both countries are looking to reap political and economic benefits during the visit", said Yury Barmin, an expert at the Russian International Affairs Council.
Saudi Arabia's ministry of information called the visit by 81-year-old Salman "historic" as it would be the first official visit to Russian Federation by a Saudi monarch.
Russian President Vladimir Putin distanced himself from President Donald Trump on Wednesday, dismissing the USA president as a man he's met once but has no personal relationship with.
Alexander Dyukov, CEO of Gazprom Neft, commented: "Given the ongoing macroeconomic uncertainties, it is of paramount importance that major oil producers coordinate their activities to improve the stability of the global oil and gas market".
At the same time, Russian President Vladimir Putin successfully fills the "power vacuum" in the Middle East and in fact has become its new "master", Bloomberg said. Even though the United States still takes the dominant position in the Middle East, the adherence of the region to traditional alliances has been weakening recently while regional leaders try to look for alternatives.