U.S. energy production has benefited many investors. Despite the rosy outlook, energy companies must continue innovating and seizing opportunities. Below are three examples of U.S. energy companies doing just that.

From maintenance to growth
Traditionally, Vanguard Natural Resources (NASDAQ: VNR) doesn't actively drill wells for production growth. Rather, Vanguard's business model is to buy and operate assets that require limited capital expenditures. That is, Vanguard buys mature producing assets that have slow, stable decline rates. Money spent goes to maintaining production, but not much more.

That past strategy has paid off. Vanguard's record of distributions is one of unending annual increases since 2007. The company currently pays $2.52 a unit for a yield of 8.1%. The company is an income investment. The stock has been generally flat since 2011 but has moved up about 10% since December and currently flirts with its 52-week high.

An innovation for Vanguard's business strategy could precipitate a substantial increase in distributions. Vanguard began actively drilling for natural gas with the intention of growing production rather than simply maintaining it. True to Vanguard's conservative nature, the Pinedale and Jonah Fields shale formations in Wyoming are safe gas plays. Vanguard is also working with Ultra Petroleum and QEP Resources, two outfits with experience in shale gas and oil exploration, rather than going it alone. So far, exploration results show promise. A company spokesman indicated an update should be available in about five weeks.

Midstream expansion
Between the Marcellus natural gas shale play, the many customers of New England and the Atlantic Coast, and at least two approved liquefied natural gas export facilities lie pipelines operated by Williams Companies (NYSE:WMB). Williams also operates natural gas pipelines connecting the Rocky Mountains to the Pacific Northwest. Despite growing natural gas production, particularly in the Marcellus, Williams' earnings growth has been less than stellar. Anemic might be a better word.

That anemic growth could quickly change. Williams recently announced it's plunking down $6 billion to acquire a greater share of Access Midstream Partners than it already owns. This move will give Williams more assets in the Marcellus and Niobrara plays, where it already has pipelines, and a new presence in Texas and Oklahoma. The move comes after Williams agreed to add two activist members to its board in response to investor criticism over its lackluster financial performance.

Investors clearly liked the Access deal, causing Williams stock to pop 20% after it was announced. An important feature of the Access deal is the business model. All of Access' business contracts are 100% fee based. This means Access has no direct exposure to the fluctuating prices of natural gas. Access also claims a 48% compound annual growth rate in its earnings before taxes, depreciation, and amortization and an 18% growth rate in its distributions.

New markets
One big growth opportunity for investors is natural gas burning engines. At current prices, natural gas offers drivers a cheaper fuel compared to diesel or gasoline. For owners of fleet vehicles, such as delivery trucks or municipal passenger buses, natural gas as a vehicle fuel makes a compelling case. One manufacturer of natural gas burning engines is Power Solutions International (OTC:PSIX).

Power Solutions offers natural gas burning engines for a variety of applications: forklifts, onsite power generation, and a variety of on-road and off-road vehicles. The company designs and builds most of the engines it sells while also modifying engines built by others. One key feature that keeps Power Solutions growing is the flexible fuel nature of many of its engines. That is, Power Solutions offers engines that burn natural gas, propane, and gasoline. This allows more fueling options for its customers, a particular advantage given the limited build out so far of natural gas fueling stations.

A recent acquisition gives Power Solutions entrance into the very large generator market. Specifically, Professional Power Products, a company that designs and builds power-generation systems, was acquired by Power Solutions. This acquisition should add $40 million to Power Solutions' 2013 sales of $238 million. Additionally, Power Solutions envisions another $1 million savings in supply chain expenses. Given Power Solutions' relationships with the likes of General Electric, even more sales volume may be in the pipeline.

Final Foolish thoughts
U.S. energy production is booming, and investors are making money off it. However, like any business, energy companies can't rest on their laurels. While all three companies offer investors compelling stories and new developments, I'm particularly bullish on Williams and its Access acquisition. This will be an immediately accretive addition and may signal a more aggressive business culture in the company. With natural gas production, consumption, and exports projected to grow, the Access acquisition and new board members could jolt Williams out of its past anemic performance.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.