Which country decided to withdraw from the Organization of the Petroleum Exporting Countries (OPEC) with effect from January 2019?

Introduction / Context:
This question tests current affairs awareness about developments in the global oil market and the role of the Organization of the Petroleum Exporting Countries, commonly called OPEC. Knowing which country decided to withdraw from OPEC with effect from January 2019 helps candidates link news events with their impact on energy politics, oil prices, and international economic relations. Such questions are very common in banking, civil services, and other competitive examinations where recent international events are important.

Given Data / Assumptions:
- The question specifically asks about a decision to withdraw from OPEC that came into effect in January 2019.
- The answer options list four countries that have been associated with oil production and OPEC membership at different times: Gabon, Angola, Saudi Arabia, and Qatar.
- We assume the question refers to the widely reported decision announced in late 2018 and implemented from 1 January 2019.

Concept / Approach:
To answer this, we must recall which OPEC member publicly announced that it would leave the cartel from January 2019. The relevant concept is basic international economic organization knowledge. OPEC is a group of oil producing countries that coordinate production policies. A member leaving OPEC is a significant news event. The correct approach is to connect the year 2018 announcements with the effective withdrawal date of January 2019 and identify the relevant country from the options.

Step-by-Step Solution:
Step 1: Recall which country publicly declared its intention to leave OPEC around late 2018. Step 2: News reports at that time clearly stated that Qatar announced it would exit OPEC to focus more on natural gas production and its long term strategy in liquefied natural gas. Step 3: The withdrawal was scheduled to take effect from 1 January 2019, meaning that from that date the country would no longer be counted as an OPEC member. Step 4: Compare this information with the options. Saudi Arabia remains a core and influential OPEC member. Angola and Gabon have had membership changes but did not announce withdrawal at that specific time. Qatar, however, matches the description exactly. Step 5: Therefore, the only option that fits the given time frame and fact pattern is Qatar.

Verification / Alternative check:
As an additional check, remember that Qatar is a relatively small crude oil producer compared to its natural gas dominance. The decision was widely interpreted as a strategic move to concentrate on gas, where Qatar is a leading global exporter. News headlines at the end of 2018 repeatedly mentioned that Qatar would leave OPEC from January 2019. No similar headlines appeared for the other listed countries at that time, which confirms that Qatar is the correct answer.

Why Other Options Are Wrong:
Gabon: Although Gabon has had changes in OPEC membership historically, it was not the country that publicly announced a withdrawal effective in January 2019, so this option is incorrect.
Angola: Angola continued as an OPEC member and did not make a high profile announcement of leaving in that period, so it does not match the question details.
Saudi Arabia: Saudi Arabia is one of the founding and leading members of OPEC and has never withdrawn. It continues to play a central role, so this option is clearly incorrect.

Common Pitfalls:
A common mistake is to confuse this fact with general information about which countries are major crude oil producers. Another error is to assume that a country with disputes over oil output may have left OPEC, without remembering the specific year and event. Candidates may also mix this up with older membership changes of smaller producers. To avoid such confusion, always connect the event to the exact time reference given in the question and recall that the news story about withdrawal effective January 2019 was specifically about Qatar.

Final Answer:
The country that decided to withdraw from OPEC with effect from January 2019 was Qatar.