| Year | Opening stock | Additions | Depletion | Revaluation adjustment | Closing stock (1+2-3+4) |
| (1) | (2) | (3) | (4) | (5) | |
| 1958 | 19.4 | 0.4 | 0.4 | -0.1 | 19.2 |
| 1959 | 19.2 | .4 | .4 | .8 | 19.9 |
| 1960 | 19.9 | .2 | .5 | .6 | 20.2 |
| 1961 | 20.2 | .6 | .5 | .4 | 20.7 |
| 1962 | 20.7 | .7 | .5 | .4 | 21.4 |
| 1963 | 21.4 | .8 | .5 | .6 | 22.2 |
| 1964 | 22.2 | .9 | .6 | -.9 | 21.7 |
| 1965 | 21.7 | .9 | .6 | -.8 | 21.3 |
| 1966 | 21.3 | .8 | .6 | -.7 | 20.7 |
| 1967 | 20.7 | .7 | .5 | -.7 | 20.2 |
| 1968 | 20.2 | .8 | .5 | -.1 | 20.4 |
| 1969 | 20.4 | .6 | .6 | .9 | 21.3 |
| 1970 | 21.3 | .7 | .6 | 2.3 | 23.7 |
| 1971 | 23.7 | .8 | .7 | 2.7 | 26.6 |
| 1972 | 26.6 | .9 | .8 | 2.5 | 29.2 |
| 1973 | 29.2 | 1.1 | .9 | 9.4 | 38.7 |
| 1974 | 38.7 | 2.2 | 1.4 | 17.5 | 57.1 |
| 1975 | 57.1 | 3.0 | 2.1 | 21.0 | 79.1 |
| 1976 | 79.1 | 3.8 | 2.9 | 16.1 | 96.1 |
| 1977 | 96.1 | 5.7 | 3.3 | 9.2 | 107.7 |
| 1978 | 107.7 | 1.0 | 3.3 | 4.8 | 110.3 |
| 1979 | 110.3 | 18.8 | 4.1 | 9.4 | 134.4 |
| 1980 | 134.4 | 11.2 | 4.7 | 10.2 | 151.2 |
| 1981 | 151.2 | 4.0 | 5.0 | 8.6 | 158.9 |
| 1982 | 158.9 | 9.7 | 5.3 | 5.7 | 169.0 |
| 1983 | 169.0 | .2 | 5.2 | 6.5 | 170.4 |
| 1984 | 170.4 | 8.0 | 6.1 | 3.0 | 175.3 |
| 1985 | 175.3 | 9.7 | 6.1 | 1.1 | 180.0 |
| 1986 | 180.0 | 9.2 | 6.2 | .3 | 183.4 |
| 1987 | 183.4 | 5.3 | 6.4 | -1.5 | 180.8 |
| 1988 | 180.8 | 6.9 | 6.3 | -6.4 | 174.9 |
| 1989 | 174.9 | 5.4 | 6.3 | -4.2 | 169.7 |
| 1990 | 169.7 | 8.2 | 6.5 | -2.0 | 169.3 |
| 1991 | 169.3 | 5.5 | 6.3 | -1.2 | 167.3 |
