could overbill
Regular verb: overbill - overbilled- overbilled

Affirmation 	
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I could overbill
you could overbill
he could overbill
we could overbill
you could overbill
they could overbill 	I could be overbilling
you could be overbilling
he could be overbilling
we could be overbilling
you could be overbilling
they could be overbilling	I could have overbilled
you could have overbilled
he could have overbilled
we could have overbilled
you could have overbilled
they could have overbilled	I could have been overbilling
you could have been overbilling
he could have been overbilling
we could have been overbilling
you could have been overbilling
they could have been overbilling	

Negation 	
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I couldn't overbill
you couldn't overbill
he couldn't overbill
we couldn't overbill
you couldn't overbill
they couldn't overbill 	I couldn't be overbilling
you couldn't be overbilling
he couldn't be overbilling
we couldn't be overbilling
you couldn't be overbilling
they couldn't be overbilling	I couldn't have overbilled
you couldn't have overbilled
he couldn't have overbilled
we couldn't have overbilled
you couldn't have overbilled
they couldn't have overbilled	I couldn't have been overbilling
you couldn't have been overbilling
he couldn't have been overbilling
we couldn't have been overbilling
you couldn't have been overbilling
they couldn't have been overbilling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I overbill?
could you overbill?
could he overbill?
could we overbill?
could you overbill?
could they overbill? 	could I be overbilling?
could you be overbilling?
could he be overbilling?
could we be overbilling?
could you be overbilling?
could they be overbilling? 	could I have overbilled?
could you have overbilled?
could he have overbilled?
could we have overbilled?
could you have overbilled?
could they have overbilled? 	could I have been overbilling?
could you have been overbilling?
could he have been overbilling?
could we have been overbilling?
could you have been overbilling?
could they have been overbilling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I overbill?
couldn't you overbill?
couldn't he overbill?
couldn't we overbill?
couldn't you overbill?
couldn't they overbill? 	couldn't I be overbilling?
couldn't you be overbilling?
couldn't he be overbilling?
couldn't we be overbilling?
couldn't you be overbilling?
couldn't they be overbilling? 	couldn't I have overbilled?
couldn't you have overbilled?
couldn't he have overbilled?
couldn't we have overbilled?
couldn't you have overbilled?
couldn't they have overbilled? 	couldn't I have been overbilling?
couldn't you have been overbilling?
couldn't he have been overbilling?
couldn't we have been overbilling?
couldn't you have been overbilling?
couldn't they have been overbilling?