A group of companies drill in the deep water Gulf of Mexico, all using more of less the same rigs and equipment (Transocean, etc.).
Shell is far from alone with deepwater finds in the Gulf of Mexico.
The Exxon-Mobil Hoover-Diana field. May 2000, was a discovery; in 2001 Union Oil drilled in 9700 feet of water, and Marathon to 7700 feet. Shell drilled in 5300 feet of water in 1997.
Chevron and BP both drilled to total depths 30,000 feet and more.
In 2004, 16 wells were drilled in water depths of 7500 feet or more.

The art is in selection of lease blocks. This depends upon interpretation of deep seismic data (a group of university trained engineers and geologists, backed by a cadre of computer wizards, market analysts (will a discovery yield a good return on investment?), etc., and the amount of money the company wishes to bid for the rights.
A new prospect is a gamble, because the presence of a likely structure on seismic sections is not enough to guarantee production success; incomplete porosity and poor relationships to source material may limit the amount of hydrocarbons pooled in the structure.
MMS is responsible for overseeing the drilling activity, but has been lax in enforcing rules on drilling, etc.