FACTBOX: Presidential candidates on energy issues

(Reuters) - With U.S. crude oil prices hitting record levels above $147 a barrel before retreating and retail gasoline pump prices topping $4 a gallon, energy is a major issue in the 2008 U.S. presidential contest.

Here is a look at what Democratic candidate Barack Obama and his Republican rival John McCain are saying about energy issues.

OFFSHORE DRILLING:

Obama - opposes lifting moratorium on drilling on federal lands off the U.S. coast. "At best you're looking at five years or more down the road and even the most optimistic assumptions indicate that offshore drilling might reduce the overall world price of oil by a few cents," he said.

McCain - supports tapping the estimated 18 billion barrels of oil on the U.S. outer continental shelf. "We can do this in ways that are consistent with sensible standards of environmental protection," he said.

SPECULATION ON OIL FUTURES MARKETS

Obama - proposed requiring U.S. energy futures to trade on regulated exchanges; wants more data gathered on index funds and other similar types of investors in futures markets; backs legislation directing Commodity Futures Trading Commission to investigate proposals such as increasing margin requirements; supports fully closing Enron Loophole.

McCain - has expressed concern about excessive speculation in futures markets; also supports closing Enron Loophole; supports investigations into possible market manipulation; supports reforming the laws and regulations governing the oil futures market to make them more transparent and effective.

NUCLEAR POWER:

Obama - supports nuclear power, but says disposing of nuclear waste from U.S. plants and resolving nuclear proliferation concerns are also important. "I don't think it's our optimal energy source because we haven't figured out how to store the waste safely or recycle the waste," he said.

McCain - wants to build 45 new nuclear reactors by 2030, and ultimately wants 100 new nuclear plants built in U.S. "If we're looking for a vast supply of reliable and low-cost electricity -- with zero carbon emissions and long-term stability -- that's the working definition of nuclear energy," he said.

GAS TAX HOLIDAY:

Obama - opposes temporarily lifting the federal tax on gasoline; says the suspension of the tax would save each American family less than $30. "This isn't a real solution," he said.

McCain - proposed the gas tax holiday; would divert funds from general government revenues to pay for transportation projects funded by the tax. "Let's give low-income Americans a break for the summer and realize maybe they deserve it, given the increase in food costs, given the increase in the cost of gasoline, given the increase in expenses particularly when most of them are on fixed income or even worse, having lost their jobs," he said.

CLIMATE CHANGE:

Obama - wants to cut carbon dioxide emissions to 80 percent below 1990 levels by 2050; reduce emissions to 1990 levels by 2020; require fuels suppliers to cut carbon content by 10 percent by 2020.