。
We're running out of oil.
Literal
Oil [subject-が] run-out [coming-きた] [emphasis-ぞ].
切れる means 'to run out, be used up.' ~てきた marks the change as having reached the speaker's awareness — the depletion was gradual and is now noticeable. ぞ is a masculine emphatic sentence-final particle signaling urgency or assertion.