Mumbai, March 1: Stocks today staged a pulsating post-budget rally, catching investors and even some market pundits off-guard.

Encouraged by the Union budget that did not contain any nasty surprises, the sensex surged 623 points to close well above the 18000-mark.

Other factors such as a strong growth in exports and infrastructure, positive global cues and some softening in crude prices aided the rally.

After opening higher at 17982.28, the benchmark index built on its gains throughout the trading session and there were no signs of profit booking.

The positive opening, market circles say, came as the budget fine print did not reveal any proposals that would put pressure on equities.

The sensex shot to an intra-day high of 18478.68 and thereafter ended at 18446.50, a gain of 623.10 points or 3.50 per cent — the biggest since May 2009. Similarly, the National Stock Exchange Nifty spurted 189.05 points to 5522.30.

Market capitalisation on the BSE spurted nearly Rs 1,85,549 crore to Rs 6,528,620.46 crore,

Observers said the strong rally gained strength from factors such as crude slipping from its intra-day highs after Saudi Arabia assured more supplies.

“One crucial event, the budget, did not contain any negative surprises. This was confirmed by the fine print. Moreover, there has been some softening of crude prices. These two factors played a decisive role in the rally today,’’ said Gaurav Dua, head of research at Sharekhan.

Some of the positives in the budget that have enthused investors include the lower fiscal deficit projection of 4.6 per cent for 2011-12, reduction in surcharge and the status-quo in excise duty rates. Markets had earlier feared a hike in excise duty rates.

Positive infrastructure data and good auto sales in February contributed to the rally.

However, Ambareesh Baliga, vice-president of Karvy Stock Broking, expressed his surprise at the magnitude of the rally and wondered what was responsible for it.

“I don’t know the logic behind this rally. Yesterday’s budget was not path-breaking and there were no big bang announcements. It was neutral to slightly positive,’’ he told The Telegraph.

Baliga, however, said one of the positives of today’s surge was that buying was seen from both foreign institutional investors and domestic institutions.

He feels the current rally is unlikely to sustain and that the key indices will at the most consolidate around the current levels.

Arun Kejriwal, director of KRIS, said the 623-point surge was “irrational’’ and that nothing had changed significantly over these two days to warrant such a gain.

Whether this rally is sustained over the next few days or not remains to be seen, but today’s trading session did see all the sectoral indices ending higher.

The highest surge was in the BSE Auto index, which rose 5.64 per cent, and the Bankex, which gained 4.35 per cent.

Auto counters rallied because the budget did not raise excise duties on cars or two-wheelers.

Similarly, the rise in bank stocks was on account of lower net borrowing numbers for 2011-12. This could ease the pressure on interest rates, thus helping banks.