-Oil futures fell to their lowest level in almost nine months Monday, as the Standard & Poor’s downgrade of U.S. debt highlighted the weak economic health of the world’s biggest oil consumer.

Light, sweet crude for September delivery settled down $5.57, or 6.4%, at $81.31 a barrel on the New York Mercantile Exchange, its lowest finish since Nov. 23. Brent crude on the ICE futures exchange settled down $5.63, or 5.2%, at $103.74 a barrel.

Oil futures started the day sharply lower, then extended their losses as equities sold off throughout the day. S&P’s decision to strip the U.S. of its triple-A rating had been expected, but many investors saw the move as confirmation that the U.S. economy is on a much weaker footing than previously expected.