The petrol price will increase by R1.62 a litre from Wednesday, the energy department said..
The South African National HIV, Behaviour and Health Survey is done every three years and was first completed in 2002.
The data helps the government develop five-year strategic plans to address HIV and Aids.
In the last month, researchers have visited 1000 households (about 3500 people) to conduct the survey. The HSRC hopes to reach 46000 South Africans.
However, HSRC CEO Dr Olive Shisana said yesterday that another 14000 randomly selected households need to be surveyed, but that middle class people are reluctant to be interviewed.
"They say I am too busy or they think HIV is a problem of poor people ... but it's not the case."
The study aims to collect data on HIV prevalence, the number of new infections, citizens understanding of HIV-Aids, their sexual behaviour and how many people are using anti-retrovirals.
Shisana implored white, Indian and affluent black people to take part so that the country would have sufficient data to make plans to address the epidemic.
"We are one people in one country and have a responsibility to participate as a group so that we can have a better health status as a country.
"We can't have data for particular groups of people," she said.
The study also aims to measure if people who are HIV positive and know their status have changed their sexual behaviour, according to Professor Leickness Simbayi of the HSRC.
There is "strong evidence" so far that they do decrease sexual partners or wear condoms if they know they are positive, said Simbayi.
Suburbs where households will be questioned are told in advance through flyers. Ward councillors, police and armed response companies are also alerted to the data collectors' presence.