Seadrill(NYSE:SDRL) is already one of the biggest ultra-deepwater drilling rig owners in the world and now it's putting another $2.4 billion into the market to solidify its position as a leader in offshore drilling. The company announced the order of four more ultra-deepwater rigs at $600 million each for delivery in 2015. It now has nine drillships on order, which should significantly increase revenue over the next three years. 

In 2012, Seadrill generated $4.5 billion in revenue and that could increase by nearly $2 billion with the nine rigs under construction. At the least, the company has $19 billion of revenue under contract. 

The question for investors is if the industry can handle all of this new capacity over the long term. Transocean (NYSE:RIG) has seven new ultra-deepwater rigs under construction, Ensco (NYSE:ESV) is building four, and Noble (NYSE:NE) will add five in coming years. Adding that much capacity means that $600,000 daily rates may not last forever, which would lower return on investment for everyone. 

The good news for offshore drilling
There are some positive trends for offshore drillers that could keep rates extremely high. The easy oil on land and in shallow water is mostly gone, which forces explorers to reach into shale reserves or deep water for oil. Discovered volumes in deepwater over the past decade are 41% higher than onshore or shallow water, and the industry is really just getting started. Research firm Wood Mackenzie predicts that deepwater oil and gas exploration will grow from $43 billion to $114 billion by 2022, which will drive demand for deepwater rigs. Between 2016 and 2022 they think another 95 deepwater rigs will be needed, so there's some leeway even if the industry overbuilds over the next few years. 

Foolish bottom line
Seadrill has been the most aggressive in adding ultra-deepwater capacity, and if rates remain high there will be strong returns for shareholders. I don't see evidence that dayrates are falling yet but be on the lookout for that as a sign that supply is exceeding capacity. 

Fool contributor Travis Hoium manages an account that owns shares of Seadrill. The Motley Fool recommends Seadrill. The Motley Fool owns shares of Seadrill and Transocean. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.