Gluconeogenesis occurs in fasting & starvation and occurs mainly in the liver, So the answer is liver. Fasting is lack of food for 12-18 hours Starvation is lack of food for 1-3 days or longer Glycogen of liver can maintain blood glucose for 12-18 hours. After that period, liver gluconeogenesis is the main source of blood glucose during fasting/starvation. The end product of glycogenolysis of glycogen stored in Skeletal muscles is glucose- 6- phosphate and not glucose due to the absence of enzyme glucose 6-phosphatase. Hence muscle glycogen cannot contribute to blood glucose directly. Figure below shows the role of liver in fed and fasting state under hormonal control. Fed state is mainly related to glycogen metabolism while fasted state shows process related to gluconeogenesis from gluconeogenic substrates.