“…While some argue strictly that OPEC does not show cartelisation behaviour and should not be regarded as a such (Colgan, 2014;Kisswani, 2016;Plaut, 1981;Reynolds and Pippenger, 2010), others acknowledge OPEC's nature as a cartel but with limited collusion and prices below perfect cartelisation (Almoguera et al, 2011;Huppmann and Holz, 2012;Okullo and Reynès, 2016). Domestic oil dependency and the role of oil for the international economy further complicate this debate by adding other possible objectives regarding geopolitics, welfare, and domestic stability to profit maximisation (Hochman and Zilberman, 2015;Kisswani, 2014;Schwarz, 2008). The same applies to non-monotonicities such as behaviour and effectiveness differing with the direction of price changes (Alkhathlan et al, 2014;Loutia et al, 2016) Obviously, the complicated, unclear nature of OPEC is a central challenge for modellers, who have to determine strategic objectives and the role of competition in the market.…”