The diagram below illustrate the productivity of three main fuel in the UK over a period of 19 years.
As it can be seen from the graph, the petroleum takes the first place with the biggest index, followed by natural gas and the smallest is coal. The data of coal were higher than that ones of natural gas in a first decade.
In first 5 years, the index of petroleum increased significantly to 140, which was stay at under 100 in 1981. And then, there was a fall after an experience of the next 5 years. After that, it increased steadily to about 140, from 1991 to 2000. Next, natural gas had a constant and stable increase. In 1981, it remained at about 40 and increased slowly to about 45 after 10 years. There was a moderate growth from 45 in 1991 to 100 in 2000.
Finally, the data of coal was unstable over a nineteen period experience. In 1981, it stayed at 80 and had a fall to about 40 in 1984. After that, it went up to 60 in 1986 and decreased slowly to under 40 in 2000.