Dr M.J. Stephan resided in Johannesburg in 1903, when he was in the process of becoming a naturalized citizen of the Transvaal Colony. Around 1905 he was employed as consulting engineer by a company pospecting for oil near the port of Inhambane, Mozambique. In March that year he was in England, where he read a paper before the Geological Society of London on the prospects of finding oil in the Orange River Colony (now the Free State). He mentioned various indications of oil in the Stormberg beds near Harrismith, including a blueish oil-bearing shale found in boreholes on several farms, oily tar found in dolerite dykes, and oil-bearing sandstone outcrops in some river beds. Other indications of oil had been found near Reitz. His paper was published in the Transactions of the Geological Society of South Africa (1905, Vol. 8, pp. 28-32).
A syndicate formed to prospect for oil on the Harrismith Town Lands asked him for a fresh report, in which he strongly advised them to start development work at once. He also reported positively on oil seepages on the farm "Oliefontein", in the Lindley district, for the Orange River Colony Oil and Exploration Syndicate, which planned to start drilling there during the latter half of 1906. Soon thereafter he was appointed as general manager for a period of two years by the African Oil and Mineral Developing Company Limited, which held options on some 30 000 ha in the districts of Harrismith, Lindley and Smithfield. In March 1907 he reported that the company's most promising holdings were those near Harrismith. Around 1908 he visited London again, where he was interviewed for the magazine South Africa, in which he was described as a cautious and conservative scientist. He was appointed as consultant adviser to the newly established Caledonian Oil Syndicate Limited, but in February 1909 this concern sold its rights on the Harrismith Town Lands to a London company for ?100 000.
In 1909 Stephan contributed a note on "Petrolium prospects in South Africa" to Petroleum Review (Vol. 18, p. 187). He was listed as a member of the South African Association for the Advancement of Science in 1906, with an address in Johannesburg. In 1919, after World War I (1914-1918), he returned to the Union of South Africa and during 1926 corresponded with the government about the treatment of bitumous deposits.