A blossoming friendship between Saudi Arabia and Russia is being reflected in a recent spate of deals, and signals yet another sea change in the ever-evolving global order.

The Middle Eastern kingdom has enjoyed a longstanding and broadly cooperative relationship with the U.S., dating back to the start of oil exploration within Saudi Arabia in the 1930s. The latest cast of key characters, headed by U.S. President Donald Trump and Saudi's King Salman, has established a warmer rapport than seen during the final years of former President Barack Obama's presidency when tensions developed over Saudi Arabia's stance on Iran and Yemen.

Yet cooperative links are now flourishing between the kingdom and Russia – the U.S.'s longstanding foe.

The flagship symbol of cooperation is the oil output cut agreement between OPEC and non-OPEC members, originally brokered and recently extended thanks largely to the determined efforts of Saudi Arabian and Russian representatives.

OPEC President Mohammed Barkindo told CNBC on Thursday from St. Petersburg that there was no doubt the "turning point" for the deal was when both countries decided to come together in China last year to sign a statement of cooperation that was "widely acclaimed".

"For them to decide to come together to address the challenges of the market … I think it is a welcome development by all producing countries," he asserted, adding that just this week both sides had reiterated their joint determination to work together to ensure that the oil market's volatility is tackled.