Following a session-high increase of almost 1%, oil prices increased slightly in early Asian trade on Wednesday as investors fretted about a supply shortage following Saudi Arabia and Russia's extension of their voluntary supply cutbacks through the end of the year.

Brent crude futures added 14 cents to $90.18 per barrel while US WTI futures advanced by 12 cents at $86.81 per barrel.

The three-month extension caught investors off guard because Saudi Arabia and Russia had promised to continue their voluntary reduction until October.

Till the end of December 2023, Saudi Arabia would prolong its voluntary 1 million barrels per day (bpd) oil output cut for an additional three months, the state news agency SPA reported on Tuesday, citing an official from the energy ministry.

According to a statement released on Tuesday by Russia's deputy prime minister Alexander Novak, the country has extended its voluntary agreement to lower its oil exports by 300,000 bpd until the end of this year.

The voluntary cutbacks agreed on by Saudi Arabia and Russia are in addition to the April cut that several OPEC+ countries agreed to implement through the end of 2024.