While I applaud Transocean's (NYSE: RIG) lack of an appetite for building rigs on spec, those who have ordered up deepwater rigs without contracts in hand continue to be rewarded handsomely.

First it was Pride International (NYSE: PDE), with a big five-year foray into the Gulf of Mexico with BP (NYSE: BP). Now Ensco International (NYSE: ESV) has a letter of intent for two years of deepwater drilling. Where and for whom? We'll have to wait for the contract's consummation for those details.

We do know the semisubmersible rig's expected dayrate -- a hair more than half a million dollars a day -- and aggregate revenue for the two-year period, at $372 million. Without further context, these numbers don't really mean squat, so let's drill down a bit.

At first glance, Ensco's deal might look disappointing, compared to Pride's recently signed five-year term contracts. But a closer look at that firm's agreement with Petrobras (NYSE: PBR), for example, strongly suggests that contract length and dayrates aren't the be-all and end-all of these arrangements.

Pride estimates that the construction cost of its new drillship, initially capable of operating in as much as 10,000 feet of water, will be $720 million. As with BP, this is at minimum a five-year contract, with expected total revenue of at least $916 million. I figure that Pride will make its investment back over a period of roughly four years.

Ensco's custom-designed 8500-series semisubmersibles, named for their water depth capacity (though they're upgradeable to 10,000 feet), cost a whole lot less than bleeding-edge drillships. The Ensco 8503 is expected to cost $427 million to build. After two years of drilling at the anticipated rate, Ensco will therefore have made back about 87% of the rig's construction cost. Here's the last bit of math I'll throw at you: That's nearly twice as fast as Pride's payback.

While I don't blame Fools for salivating over Atwood Oceanics (NYSE: ATW), I firmly believe that Ensco is good to go.

Related Foolishness:

Petrobras is an Income Investor pick, and Atwood is a Stock Advisor selection. You can try out either service free for 30 days.

Fool contributor Toby Shute doesn't have a position in any company mentioned. The Motley Fool has an ultra-deep disclosure policy.