Yet while unconventional production may herald the dawning of a Golden Age of Gas, it does not necessarily create an era of oil abundance. New supplies of unconventional oil will help reduce OPEC's share of supply over the next decade. Other new sources will also contribute, such as oil from Brazil...

-- Maria van der Hoeven, Executive Director, IEA, Opening remarks, WEO 2013 launch, November 12, 2013

Global energy demand is only going to increase more over time. Even with the expansion of green energy from solar and wind, the use of oil and gas to produce electricity, fuel transportation, and as a feedstock in manufacturing, will continue to expand worldwide, even as domestic consumption of oil has reduced. For investors with a long-term outlook, this presents a great opportunity for strong, decade-long returns, even investing in "Big Oil" players like ExxonMobil (XOM 0.02%) and Royal Dutch Shell (RDS.B), and more specialized companies like offshore driller Transocean (RIG -2.69%) and ultra-deepwater specialist Seadrill Limited (SDRL). Let's take a closer look.

It's all about sustainable trends

Source: IEA World Energy Outlook 2013 Launch (opens PDF)

As much as renewables, coal, and even nuclear are set to expand over the next two decades, both natural gas and oil demand will continue growing as well, meaning diversified majors like ExxonMobil and Royal Dutch Shell will continue to play vital roles in finding and developing these oil and gas resources. For Shell, this includes projects like the Carmon Creek project in Alberta, Canada, which is expected to produce 80,000 barrels per day, and be a reliable source for "more than 35 years."

ExxonMobil, along with partners ConocoPhillips and TransCanada recently announced a step forward in the Alaska LNG project, which will both increase local access to natural gas for population centers in Alaska, as well as a liquefaction facility. Total investment in this project is expected to be between $45 and $65 billion. 

Offshore is going to be increasingly important; especially deepwater and ultra-deepwater
 

Source: IEA World Energy Outlook 2013 Launch (opens PDF)

Over the next decade-plus, offshore rig operators like Transocean and Seadrill will see the demand for their services grow, as land-based resources become increasingly harder and more expensive to reach. With the unfortunate exception of investors who bought shares a few months before the Deepwater Horizon accident in the Gulf of Mexico in 2010, Transocean -- the largest contract offshore driller -- has been a great investment for more than two decades. 

However, Transocean's fleet of drillships and jackup rigs is aging; a real concern as more assets are requiring deeper drilling capabilities. Transocean is making efforts to get in front of the demand curve, with seven ultra-deepwater drillships currently under construction, and a recent announcement for what could be as many as 10 new jackup rigs. With more than 80 ships currently in the water, Transocean is the dominant player in offshore. 

Seadrill is a much smaller player, but is investing heavily (and leveraging massive amounts of debt) to grow as quickly as possible. As of last quarter's earnings, the company had more than 20 new build ships under construction or close to completion. Of these, only seven had contracts in place upon completion. Considering that the company only operates 35 ships today, if a large number of these ships aren't under contract upon completion, the cost to maintain these assets would severely impact Seadrill. Add in that the company already carries a massive amount of debt (more than $11 billion per the latest earnings statement,) and it's a reminder that an investment in Seadrill is counting on its management to make sure these rigs are put to work as soon as they hit the water. 

Final thoughts
As much as the world becomes more energy-efficient and green technologies play a larger role in our energy future, oil and gas demand will continue to grow. Take a hard look at your portfolio. Are you invested to benefit from the growth in demand over the next twenty years? If not, one or more of these companies may be a good place to start.