We carried out high-precision photometric observations of three eclipsing ultrashort-period contact binaries ( USPCBs ) . Theoretical models were fitted to the light-curves by means of the Wilson-Devinney code . The solutions suggest that the three targets have evolved to a contact phase . The photometric results are as follows : a ) 1SWASP J030749.87 - 365201.7 , q = 0.439 \pm 0.003 ,f = 0.0 \pm 3.6 \% ; b ) 1SWASP J213252.93 - 441822.6 , q = 0.560 \pm 0.003 ,f = 14.2 \pm 1.9 \% ; c ) 1SWASP J200059.78 + 054408.9 , q = 0.436 \pm 0.008 ,f = 58.4 \pm 1.8 \% . The light curves show O ’ Connell effects , which can be modeled by assumed cool spots . The cool spots models are strongly supported by the night-to-night variations in the I -band light curves of 1SWASP J030749.87 - 365201.7 . For a comparative study , we collected the whole set of 28 well-studied USPCBs with P < 0.24 day . Thus , we found that most of them ( 17 of 28 ) are in shallow contact ( i.e . fill-out factors f < 20 \% ) . Only 4 USPCBs have deep fill-out factors ( i.e . f > 50 \% ) . Generally , contact binaries with deep fill-out factors are going to merge , but it is believed that USPCBs have just evolved to a contact phase . Hence , the deep USPCB 1SWASP J200059.78 + 054408.9 seems to be a contradiction , making it very interesting . Particularly , 1SWASP J030749.87 - 365201.7 is a zero contact binary within thermal equilibrium , implying that it should be a turn-off sample as predicted by the thermal relaxation oscillation ( TRO ) theory .