This paper examines the impact of informal quotas on the substantive representation of women in appointed upper parliaments using the Omani State Council as a case study. Although no formal gender quota has been institutionalized in Oman, it is presumed that the Sultan will assign 17% of the seats to women, effectively an informal quota. Through semi-structured interviews with female MPs appointed to the State Council, I examine the relationship between informal gender quotas and the substantive representation of women. The findings reveal that the majority of appointed female MPs under informal quota acted for women's interests inside and outside the parliament. Within the parliament, they reviewed legislation with consideration to women's interests and proposed studies or drafted laws on women's issues. Outside the parliament, they acted for women's interests by tapping into their social and political capital, which is presumably acquired through their appointment to the State Council.