The final results for 44 seats are expected by tonight with as many as 132 candidates in the fray while polls for four seats were delayed by a court order.
The polling started at 9 am and was stopped for few hours due to allegation of rigging by different parties.
Four candidates have already been elected unopposed when the process for election started last month.
The Senate is a continuous body and senators are elected for six years but under the law, half of the 104-member house retire after every three years.
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The seats allocated to a province comprise 14 general seats, four reserved for women, four for technocrats and one for a minority member.
The senators are elected by provincial assembles and the national assembly.
According to the Election Commission of Pakistan, 84 candidates will contest for 33 general seats from the provinces, FATA and the federal capital, 22 for eight seats reserved for women from the provinces and the federal capital and 18 for eight seats reserved for technocrats.
The ruling Pakistan Muslim League-Nawaz (PML-N) and main opposition Pakistan Peoples Party (PPP) are expected to secure almost equal representation in the Senate.
Imran Khan's Pakistan Tehreek-e-Insaf could secure representation in the Upper House for the first time while the PPP is expected to lose its majority in the Senate polls.