Saudi Arabia's crown prince said oil firm Aramco and petrochemical firm SABIC would lead 5 trillion riyals ($1.33 trillion) of investments by the local private sector by 2030 under a programme announced on Tuesday for economic diversification.
The kingdom's benchmark index eased 0.1%, hit by a 1.5% fall in oil giant Saudi Aramco and 2% slide in Saudi Basic Industries Corp.
Qatar enters another year of its blockade by Saudi Arabia, Egypt, UAE and Bahrain on accusations of backing "terrorist" groups, charges which Doha denies.
Pharma company Moderna said on Monday its experimental vaccine was 94.5% effective in preventing the virus, which has ravaged economies across the globe.
Saudi Arabia's benchmark index rose 0.3%, with Al Rajhi Bank rising 1% and Dr Sulaiman Al-Habib Medical Services advancing 2.6%.