This acquisition of 12 more F-15SGs is part of the RSAF's continuing effort to renew its fighter fleet. The additional F-15SGs, which will be equipped with sophisticated avionics and weapon systems, will be delivered from 2010.
Link
http://app.sprinter.gov.sg/data/pr/20071022998.htm
SINGAPORE EXERCISES OPTION FOR ADDITIONAL F-15SGS
In December 2005 the Ministry of Defence announced the purchase of an initial 12 Boeing F-15SG fighter aircraft to replace the Republic of Singapore Airforce (RSAF)'s A-4 Skyhawk fighters. The Ministry of Defence has, on 22nd October 2007, exercised the option to purchase eight more F-15SG fighters which was part of the original contract signed in December 2005. Along with this buy, an additional order for four F-15SGs was made.Link
http://app.sprinter.gov.sg/data/pr/20071022998.htm