Rating agency Standard and Poor's (S&P) has recently lowered the rating of several oil and infrastructure firms in China,revising the country's credit rating from ‘stable’ to ‘negative’.S&P downwardly revised China's credit rating mainly due to "increased economic and financial risks," while the last decision on lower country's state oil and infrastructure companies also surprised markets.China has not been immune to a global glut in oil supply that has caused oil prices to fall dramatically over the last 18 months and a slowdown in the Chinese economy has weakened demand for oil,hitting markets further.