The composite face on the right is said to be keener on short-term sex
People's attitudes to relationships could be given away by just the look of their face, it has been claimed - with men and women often after the opposite.
Researchers said men generally preferred women they perceive are open to short-term sexual relationships, with women after longer-term matches.
Men with big jaws and small eyes were perceived as less committed by women.
The Universities of Aberdeen and St Andrews worked with Durham University studying 700 people in their 20s.
The scientists said their research showed people could use their perceptions to make more informed partner selection depending on the type of relationship they were after.
Heterosexual participants were shown pairs of photographs of men and women in their early 20s.
Participants were asked to choose the face that they felt would be more open to short-term sexual relationships, one-night stands and the idea of sex without love.
They were also asked which face they thought was the most attractive for a long or short-term relationship, who was more masculine or feminine, and who they thought was generally attractive.
These judgments were compared with the actual attitudes to relationships of the subjects in the photographs determined through a questionnaire.
Researchers said that the results determined many could accurately judge from photographs who would be more interested in a short-term sexual relationship or a long-term relationship.
Women who were open to short-term sexual relationships were usually seen by others as more attractive.
The left face is said to be generally keener on long-term relationships
The men who were more open to casual sex were generally perceived as more masculine-looking, with squarer jaws, larger noses and smaller eyes.
Dr Lynda Boothroyd, of Durham University's psychology department, told the BBC Scotland news website: "This study shows we can make these kind of instinctive judgements for sex. We have a subconscious - not always right but reasonable - guide."
She explained: "Our results suggest that although some people can judge the sexual strategy of others simply from looking at their face, people are not always sure about their judgements possibly because the cues are very subtle.
"Yet preferences for different types of face were actually quite strong. This shows that these initial impressions may be part of how we assess potential mates - or potential rivals - when we first meet them.
"These will then give way over time to more in depth knowledge of that person, as you get to know them better, and may change with age."
Dr Ben Jones, of the University of Aberdeen's Face Research Lab, said: "Lots of previous studies have shown that people can judge a lot about a person from their face, including things like health and even some personality traits like introversion.
"But this really is the first study to show that people are also sensitive to subtle facial signals about the type of romantic relationships that others might enjoy."
Professor David Perrett, a psychologist from the Perception Lab at the University of St Andrews, added: "While faces do hold cues to sexual attitudes, men should not presume any kind of relationship is wanted from appearance alone since women's choice is what matters.
"Indeed most women found promiscuous-looking guys unattractive for both short and long-term relationships."
The study, published in the Journal of Evolution and Human Behaviour on Wednesday, was funded by the Medical Research Council and the Economic and Social Research Council.