Most banks in Singapore offer mortgage packages that are pegged to either SIBOR or SOR rates.
Singapore Interbank Offered Rate (SIBOR) is a daily reference rate based on interest rates at which banks offer to lend unsecured funds to other banks in the Singapore wholesale money market.
Singapore Swap Offer Rate (SOR) is an FX-implied rate and is calculated from a formula that includes USD/SGD forward rate and USD/SGD spot rate.
Recent trends reflects that SOR has been considerably lower than SIBOR since 2008. In fact, SOR fell to a negative value in 2011.
Despite that, do note that historically, SOR spent more time above SIBOR than below it.
It is generally considered that SIBOR is more stable, while SOR is more volatile.
This is due to the fact that SIBOR is based on rates in which financial institutions lend to other financial institutions, while SOR is based on USD interest and exchange rates
Although SIBOR and SOR rates are affected by different factors, they ultimately move in the same general direction together.
Whatever the micro or macro economy situation is, if SIBOR were to go up, SOR will move up too.