The 21, who include both expatriates and Nigerians, are being questioned in Abuja, while the top bosses are in Lagos, officials say.
The authorities raided Halliburton’s office in Lagos last week, seizing documents and detaining 10 people – eight of them Nigerians and two expatriates. They have been released as investigations continue.
The Halliburton executive is to be questioned over an alleged 182 million dollar (140 million euro) cash-for-contracts scandal which involved the construction of a liquefied natural gas planet in southern Nigeria.
In October Adeyanju Bodunde a personal aide to ex-president Olusegan Obasanjo was charged in a probe linked to the case.
Halliburton has been at the centre of controversy over an alleged conflict of interest by George Bush’s vice-president Dick Cheney at the time of the Iraq invasion.
In 2007 former Nigerian petroleum minister Dan Etete was found guilty of accepting bribes by a French court and various other politicians and officials have been accused of being involved in graft. He was living in Britain at the time and another French court later found him guilty of money-laundering.
Shell is being investigated over recent cases brought in the US over bribes paid around the world. Oil services companies and Swiss freight-forwarding company Panalpina World Transporting Holding Ltd agreed to pay 48 million dollars (37 million euros) to settle the cases.
Shell officials in Nigeria say the company will cooperate but refused to comment in detail.
Nigeria is one of the world’s largest oil exporters.