Share of European cruise market

Carnival 9% Royal Caribbean 6% Princess 25%

This is some way short of the outright majority needed to secure an adjournment, but the announcement has upped the ante in the takeover battle.

Successfully putting off the Royal Caribbean vote would give Princess shareholders more time to weigh up Carnival's rival bid.

It would also delay a final decision until after competition watchdogs in Europe and the US have decided whether or not there are grounds for blocking either deal.

Regulatory uncertainty

All along, Princess' main objection to the Carnival bid has been that it would be less likely to obtain regulatory clearance, especially in Europe.

However, some observers argue that this depends on whether the European Commission assesses the impact of the proposed mergers on the cruise liner market, or on the wider market for holidays.

If the Commission chooses the holiday market as its benchmark, then both mergers are expected to gain clearance.

Cruises have enjoyed strong growth in recent years

But if it makes its decision by reference to the luxury cruise market, the institution is thought more likely to impose conditions on the Carnival/Princess merger due to its greater market share.

However, obtaining complete regulatory clearance for the Princess/Royal tie-up will not be plain sailing either.

Last month, the UK's Office of Fair Trading referred the Princess/Royal merger to the Competition Commission.

Supporters of the Carnival bid believe that the UK probe undermines Princess's claim that the tie-up with Royal carries less regulatory risk, and strengthens the case for adjourning Thursday's vote.

Royal gamble

An adjournment, although not enough in itself to blow the Princess/Caribbean merger off course, would greatly strengthen Carnival's hand.

It would give Carnival - currently banned under UK Takeover Panel rules from upping its bid again until after the 14 February meeting - an opportunity to put together a more tempting offer.

More importantly, any firm sign that Princess is starting to consider alternative offers could prompt Royal - which has already shown signs of impatience at Princess's new dalliance - to pull out of the original merger deal.

A leading member of Royal's board said last week that he would consider a vote for an adjournment to be "tantamount to a vote for Carnival."

Princess would, of course, prefer to keep its options open.

If Royal walked away, and an alternative tie-up with Carnival deal was then blocked by regulators, the company would be back to square one, probably leaving shareholders nursing hefty losses.

On the other hand, it is by no means certain that Royal would pull out in the event of an adjournment.

Royal, whose smaller size means that it is even more vulnerable to the slowdown in global tourism spending, may decide that it would be better to swallow its pride and wait in the hope that the regulator's verdict goes its way.

But the St Valentine's Day vote provides a good example of how an investment decision can sometimes resemble a gamble.