You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
1973_oil_crisis

Context:
This contributed to the "Oil Shock". After 1971, OPEC was slow to readjust prices to reflect this depreciation. From 1947 to 1967, the dollar price of oil had risen by less than two percent per year. Until the oil shock, the price had also remained fairly stable versus other currencies and commodities. OPEC ministers had not developed institutional mechanisms to update prices in sync with changing market conditions, so their real incomes lagged. The substantial price increases of 1973–1974 largely returned their prices and corresponding incomes to Bretton Woods levels in terms of commodities such as gold.

Question:
When did OPEC start to readjust oil prices?

After 1971