1 Btu is an insignificant amount of energy. When discussing output of a single power plant we would use the units of millions of Btu's. When discussing national or international energy consumption we use the units of quadrillion Btu's. Quadrillion = 1,000,000,000,000,000
The unit Btu allows us to compare different sources of energy. In this example we see that a barrel of oil is cheaper than a ton of coal. However, a ton of coal produces more energy and the actual cost of energy is less for coal. We can also use Btu's to compare the environmental effects of different types of energy. One example would be comparing the amount of SO2 emissions per Btu for different types of coal.
Resources are always higher than reserves. An example of an energy resource would be the oil and gas of the Arctic National Wildlife Refuge in Alaska. This area has not been thoroughly explored so the exact amount of oil and gas is unknown. Economically the cost of developing these resources is high . In addition, for conservation reasons this area is off limits.Changes in the political or economic climate can cause resources to become reserves and vise versa. The oil embargo of the 1970's raised the price of oil which resulted in the development of a number of new oil and gas fields. In order to reach it's goal of energy independence, the Carter administration offered tax breaks to companies as incentives to developing new production techniques such as secondary recovery. As a result a number of marginal oil fields (Resources) became economical (Reserves).