Gavi, the Vaccine Alliance, said another £57m ($90m) may be provided to help countries distribute the vaccines and rebuild devastated health systems.
A decision about which vaccine to use will be taken in light of results from on-going clinical trials.
Two manufacturers have vaccine candidates at an advanced stage of development and others are in the pipeline, with more trials thought to be on the way.
The Gavi board’s purchase commitment was made before a vaccine recommendation from the World Health Organisation (WHO) in order to reduce risks from delays in rolling out treatment.
Gavi chief executive Dr Seth Berkley said: “The Ebola outbreak reminds us of the critical importance of vaccines in fighting infectious diseases.
“The board’s decision underlines Gavi’s commitment to support the people of Ebola-affected countries by ensuring that they will have access to a WHO-recommended vaccine as soon as one is approved and available from manufacturers.”
Gavi funding could also be used to create stockpiles of first and second-generation Ebola vaccines that could be rapidly deployed to combat future outbreaks.
The organisation already funds similar stockpiles of yellow fever, meningitis A and oral cholera vaccines.
Dagfinn Hoybraten, chair of the Gavi board, said: “We are making determined efforts to ensure that people living in Ebola-affected countries are protected as soon as possible and do not have to face another terrible outbreak in the future.”
The UK is one of the biggest contributors to Gavi, which is funded by governments and the Bill & Melinda Gates Foundation.
A Swiss pilot trial of one Ebola vaccine being co-developed by the drug company Merck has been put on hold as a precaution after a number of participants complained of joint pains in their hands and feet.
Ebola has so far infected 17,145 people since the current outbreak began in Guinea in December 2013, according to the WHO. The disease has caused 6,070 reported deaths.
The UN Ebola chief has said it will take several more months before the outbreak in West Africa is under control, an assessment that makes clear the UN’s goal of isolating 100 per cent of Ebola cases by January 1 will not be met.
Dr David Nabarro said there has been “a massive shift” over the last four months in the way affected governments have taken the lead in responding to the epidemic, communities are taking action and the international community has pitched in.
But he said greater efforts are needed to combat Ebola in western Sierra Leone and northern Mali, to reduce the number of new cases in Liberia and to limit transmission to Mali.
The WHO conceded that it did not meet an interim December 1 target of isolating 70 per cent of Ebola patients and safely burying 70 per cent of victims in hardest-hit Sierra Leone. But it has not made clear what that means for the January 1 goal of 100 per cent of cases isolated and bodies buried safely.