T_e(OIII)–T_e(OII) plane containing our 130 systems with direct Z_Te estimates [i.e. those for which both T_e(OIII) and T_e(OII) can be calculated from auroral lines]. Six empirically- or theoretically-derived T_e(OIII)–T_e(OII) relations from Campbell et al. (1986, black), Pagel et al. (1992, orange), Izotov et al. (2006, blue, for metallicities of 7.2, 7.6, and 8.2), Pilyugin et al. (2009, red), López-Sánchez et al. (2012, grey), and Andrews & Martini (2013, green, as defined in Ly et al. 2016a), are also plotted for comparison. Our dataset reveals a much broader distribution of T_e(OII)/T_e(OIII) ratios than is expected from the literature relations.