A global economic downturn, lower but lately rising oil prices and an aggressive U.S. environmental agenda have made for one of the most bewildering energy investment landscapes in decades.

Oil prices whipsawed from nearly $150 a barrel to $30 a barrel in a matter of months and have climbed back up around $65, amid signs of economic recovery that could revive demand.

But big oil companies like Exxon Mobil (XOM.N: Quote, Profile, Research, Stock Buzz) say it's still too early to declare an end to the economic slump and the first plunge in world energy demand in a quarter century.

The price collapse was so sudden that a lot of them got caught flat-footed, said Nauman Barakat, senior vice president of Macquarie Futures USA.

They're going to be a lot more reluctant this time around even if prices jump back to $70 or $80, Barakat said. The concern will be, 'Is this going to be fleeting or a little bit longer lasting?'.

Meanwhile, the Obama administration has been pushing U.S. climate, alternative energy and fuel efficiency proposals that could fundamentally change the sector's economic equation.

The biggest market for fossil energy in the world is about to become the second biggest market for emissions allowances in the world, said Kevin Book, a managing director and senior analyst at ClearView Energy Partners LLC.

Obama is asking Congress for the first-ever U.S. limits on heat-trapping carbon dioxide emissions as well as fuel changes to reduce vehicle emissions. It changes your price structure, Book said

With these questions looming, more than 40 top industry officials will meet with Reuters journalists in Houston, London and Singapore next week for an exclusive, in-depth discussion.

Among the top guests are U.S. Energy Secretary Steven Chu representing the world's top energy consumer and OPEC Secretary General Abdullah al-Badri representing the cartel of nations that produce about a third of the world's oil.

The industry faces questions about where and how to invest in future supply as its biggest market, the United States, becomes less dominant and places like China and India become more important in the world economy and energy markets.

The message is look to your global markets. The growth now is going to be somewhere else. Play defense at home and go on offense overseas, Book said.

The path forward is more difficult because Obama's energy and environment programs have built-in conflicts, Barakat said. Exporting countries are being asked to deliver more oil and gas at the same time the United States is trying to cut fossil-fuel dependence.

If you're encouraging diversification and a move away from OPEC and oil, what incentive is there for, say, Saudi Arabia to sink billions of dollars into new exploration and production? Barakat said.

Still, economic recovery should make investment easier because energy demand is not going away, he said.

As economies improve, that should pull up oil prices, should help producers sink more money in, Barakat said. But when that will happen is a huge question mark, he said.

(Reporting by Bruce Nichols; Editing by David Gregorio)