"MTN, Globacom and Airtel paid at the close of work on Monday this week, while Etisalat paid at the close of work on Tuesday," Nigerian Communications Commission (NCC) sources who opted to remain anonymous told PTI on the phone.
NCC had penalised the four operators in the country for poor quality of services after a Key Performance Indicators (KPIs) test carried out on their networks for the months of March and April.
The Managing Director and Chief Executive Officer of Airtel Nigeria, Rajan Swarup confirmed to PTI that his company has paid the fine.
Last month, NCC spokesman Reuben Muoka had said the four operators failed to meet with the minimum standard of quality of service.
The NCC had arrived at the decision on testing the operators on four parameters -- Call Set-up Success Rate, Call Completion Rate, Drop Call Rate and Traffic Channel Congestion.
Nigeria has a population of 150 million making mobile telephony a highly profitable venture but customers often complain of poor services.
Many people prefer to carry more than one phone so they could have an alternative connections when one fails.
However, the operators blame the bad quality of services on poorly developed infrastructure like electricity which, they say makes it cumbersome to deliver services to subscribers.
Nonetheless, Airtel Nigeria, which started operations in 2010 was awarded as the best GSM operator in the country, 2012 by NCC.