Abstract: In 1959, Somerton published a paper in the AIME Petroleum Transactions on a laboratory study of rock breakage by rotary drilling. The paper made an attempt at correlating unconfined compressive strength of rock to non-dimensional groupings of drilling parameters measured in controlled laboratory experiments. The results using small-scale concrete specimens and two natural rocks revealed that a combination of drilling parameters could be used to estimate a drilling strength rather than an unconfined compressive strength. A discussion of Somerton’ s paper by Simon (1959) showed that Somerton’ s expression was a special case of the general expression, which could be applied to all drilling types rather than just rotary drilling. The work of both Somerton and Simon highlights the importance of drill bit design and wear, which directly affects the rate of penetration and bit efficiency. This paper revisits the work initiated by these authors and investigates how it can also be applied to rock coring and potentially extended to unconsolidated materials by incorporating drill bit characteristics and measured torque during borehole advance. By applying these historical equations to field-collected data, this paper provides some insight into their practical implications, highlights the need for careful interpretation of empirical correlations in MWD analysis and emphasizes the importance of unit consistency.