The chart illustrates the output of petroleum, coal and natural gas in the UK from 1981 to 2000. It's obvious that 
around 
the year Change preposition
apply
of 
1991 was a big turning point for these three kinds of fuelChange preposition
apply
,
 since all of them had huge differences after the year.
From 1981 and 2000, petroleum showed a Remove the comma
apply
dominate
 Replace the word
dominant
production
 level among these three kinds of fuel, though it experienced some fluctuation during Use synonyms
this
 period. In 1981 the Linking Words
energy
 Use synonyms
units
 of petroleum kept a significant upward trend until 1984Use synonyms
,
 and Remove the comma
apply
stay
 at around 140 Wrong verb form
stayed
energy
 Use synonyms
units
 from 1984 to 1987. Use synonyms
Then
 it dramatically Linking Words
fall
 to 100 Wrong verb form
fell
energy
 Use synonyms
units
 in 1990. And after Use synonyms
that
 the Add a comma
that,
production
 bounced back at around 1991Use synonyms
,
 and had Remove the comma
apply
steady
 increase Add an article
a steady
at
 the rest of the years.
The Change preposition
in
production
 of coal and natural gas seems steadier between 1981 and 1991. Except for a sudden drop Use synonyms
by
 coal, which was from 80 to about 36 Change preposition
in
energy
 Use synonyms
units
. Use synonyms
Then
 it quickly Linking Words
recover
 to about 60 Change the verb form
recovers
energy
 Use synonyms
units
 by the year Use synonyms
of 
1986, and Change preposition
apply
at
 the following years until 1991, the Change preposition
in
production
 is steady but a small decrease from 1989 to 1991. After 1991 the Use synonyms
production
 of Use synonyms
these two fuel
 showed Change the determiner
this two fuel
these two fuels
complete difference
 tendencies, Replace the word
completely different
which
 natural gas substantially climbed up and surpassed the Change preposition
in which
production
 of coal, Use synonyms
while
 coal still suffered a decline Linking Words
at
 the rest of the period.Change preposition
for