Election Commission (EC) secretary-general Puchong Nutrawong said that in Bangkok a reception room at Parliament Building No 2 is being used as the venue for registration.
In other provinces, the venues are fixed by the election committee in each province.
Five candidates showed up before 8.30am at the parliament building in Bangkok for registration. However, only three of them had all the required documents. They are Pol Maj Gen Supisarn Bhakdinarunart, who resigned as commander of Crime Suppression Division to run in the poll; Srisuwan Janya, president of the Anti-Global Warming Association; and Leena Jangjanya, or Leena Jang, a businesswoman and lawyer.
In the drawing of numbers, Pol Maj Gen Supisarn picked No 1, Mr Sriwuan No 2 and Ms Leena No 3.
Veera Yeeprae, director of the Bangkok election committee, said each candidate in Bangkok can appoint 500 assistants, 10 in each of the 50 districts. Each of them can spend no more than five million baht on their campaign, which is limited to self-introductions and explaining his or her vision.
Each candidate vying for election to the Senate must be a Thai national, at least 40 years old, with at least a bachelor's degree or equivalent education. He or she must have had a domicile registration or received schooling in the province for at least five years, or been born in the province.
The other members of the 150-seat Senate are appointed.