Shell D'Arcy Petroleum Development Company (the Anglo-Dutch venture later restructured as Shell-BP and ultimately as Shell Petroleum Development Company of Nigeria) drilled the discovery well Oloibiri-1 in present-day Ogbia LGA of Bayelsa State, completing it on 15 January 1956 at a total depth of 12,008 feet. Commercial production began on 17 February 1958 from the Oloibiri field at an initial rate of 5,100 barrels per day. The first crude cargo — 8,400 long tons of Bonny Light — was exported from the new Bonny Terminal on 17 February 1958 aboard the BP tanker Hemifusus, bound for Rotterdam.
The fiscal architecture of the federation was at that moment still overwhelmingly agricultural: in 1958/59 the four regional Marketing Boards (Cocoa, Groundnut, Palm Produce, Cotton) controlled roughly 70% of foreign-exchange earnings, and federal revenue was dominated by import and excise duties collected at the southern ports. Oil contributed less than 1% of total exports in 1958.
The inversion proceeded over the following twelve years on the back of further discoveries — Afam (1957), Bomu (1958), Imo River (1959), Ughelli (1959), Forcados Yokri (1968), Egbema (1969) — and the construction of the Trans-Niger and Trans-Forcados pipeline systems. By 1965 oil was 25% of exports; by 1970 it had overtaken agriculture; by 1974, the year after the OPEC price quadrupling, oil and gas were over 80% of foreign exchange and over 70% of federally retained revenue; by 1980 they were over 95% and 80% respectively. The Petroleum Profits Tax Ordinance 1959 — passed in the late colonial period to capture the new rents at a 50/50 split — was the architecture on which the federation came to depend.