High percentage of monounsaturated triacylglycerols (having acyl chains with only one double bond), as in the case of
Peanut oil, have high melting points. This is because carbon skeleton lay very nicely on top of each other. Due to this they have relatively stable structure. Ofcourse, the structure as stable as a perfectly crystalline materials. Hence, these compounds have higher melting points. Due to this,
peanut oil freezes in cold conditions.
On other hand, higher percentage of polyunsaturated triacylglycerols (having acyl chains with more than one double bond), as in case of vegetable oil, have single or multiple double bonds in tandem. Due to these bonds, the successive layers of vegetable oils are not able to properly align with respect to adjacent layers. Hence, they low melting points. Due to this, they remain liquid state, even in cold conditions.