For much of the past century, technological advances in locating and producing oil -- gas was essentially a byproduct during most of that time -- came at a relatively slow, steady rate. Since then, as you know, two key approaches have been developed to vastly enhance our ability to increase the output of both crude oil and natural gas.

Obviously, one of these innovations is fracking, which has permitted us to coax gas and oil from previously impenetrable shale formations. The other is the ability to drill for and produce oil in the ultra-deepwater, 7,500 feet or deeper. In addition to far more sophisticated and costly rigs, working in the ultra-deepwater requires new ways to complete and produce from deep wells, along with the capability of attending to, troubleshooting, inspecting, and repairing downhole and subsea equipment nearly two miles beneath the sea's surface.

Access to the ultra-deepwater has breathed new life into the once declining Gulf of Mexico, and has facilitated major activity in places like offshore Brazil and West Africa. The importance of the deepwater can only increase, making it vital for energy investors to keep abreast of those companies that make things happen way down low. Let's take a look at three of the leaders:

Cameron International (CAM.DL)
As with many oil-field service companies, Houston-based Cameron International is the survivor of several mergers. Today, Cameron manufactures a host of valves, pumps, wellheads, risers and other equipment used in drilling and production. Perhaps more importantly, it makes components for land and offshore rigs, along with subsea production systems and all-important blowout preventers.

As June came to an end, the company finalized a joint venture, OneSubsea, with Schlumberger (SLB 0.67%). The intriguing partnership -- in which Cameron has a 60% interest, with the remainder Schlumberger's -- will develop products, systems, and services for the subsea oil and gas market.

Cameron's market capitalization is approximately $16 billion. The company is rated better than a buy by the analysts who follow it.

National Oilwell Varco (NOV 0.64%)
The product offerings of National Oilwell Varco, the favorite of many energy investors, overlap in several areas with Cameron's. For instance, Varco provides an array of components and equipment for drilling rigs, including derricks, cranes, and pipe-handling equipment. It also manufactures blowout preventers.

When it reports its quarterly results on July 30, National Oilwell Varco is expected to slide on an earnings per share basis to about $1.33, or down $0.13 year over year. It's dip, should it occur, will be partially tied to the process of digesting a host of acquisitions made during the past several years. Perhaps a more important number for the first quarter of 2013 was an impressive 8% backlog increase. That's a metric that clearly should be monitored in the upcoming report.

Oceaneering International (OII 6.51%)
Once a diving company, Oceaneering now operates through four separate segments: subsea projects, subsea products, asset integrity, and remotely operated vehicles. The company remains the only manufacturer of a full range of subsea umbilical systems. But it's the ROV unit that garners much of the attention for Oceaneering today.

The 9,000-pound aquatic robots are the key part of 150,000-pound units that can operate effectively in 10,000 feet of water. They're guided by three-person crews in 20-foot computerized control rooms that sit atop a rig's floor. Oceaneering's ROVs played a key role in ultimately stanching the flow of the approximately 5 million barrels of oil that gushed into the Gulf of Mexico from BP's (BP 0.71%) blown-out Macondo well in 2010.

Oceaneering's shares have somewhat quietly risen 58% in the past year and 41% during 2013.

Foolish takeaway
There are other energy companies that benefit from the increasing importance of the deepwater. However, the three five-star CAPS-rated companies discussed above are clearly in the sweet spot of the movement to greater depths. Each warrants the attention of Foolish energy investors.