The Observer, part of the Guardian News & Media stable, shed nearly 9,000 copies from the previous month, with the Sunday quality market in continuing difficulties.
The Independent on Sunday fell 2.2% to 122,588 copies and The Sunday Times dropped 0.9% to 915,969 copies.
The trend was bucked by The Sunday Telegraph, up 0.6% to 450,276 copies.
The Observer, which fell below the 300,000 copy mark in March 2011, is now at its lowest circulation since the start of ABC records in 1962.
While it is down 15.4% year on year, a Guardian News & Media source attributed some of the decline to the prior year comparative including 17,910 overseas copy sales (excepting the Republic of Ireland). The paper discontinued overseas copies in July last year.
In the Sunday tabloid market, the 50p Sun remains on a downward trend, losing 2.3% of the circulation it registered in May.
Now on 2,189,924 copies, the News International title is down almost a third from its stellar debut circulation of 3,213,613 copies registered in the final week of February.
The £1 Sunday Mirror dropped 0.5% to 1,088,354 copies, pretty much where it had been in April after a small rally in May.
Trinity Mirror stablemate The People shed 2.7% of its May circulation, landing at 450,097 copies.
Only the mid-market avoided any drops, with the Sunday Express up by the slightest of margins to 512,843 copies, but The Mail on Sunday putting in the best performance of any Sunday paper, up 1.2% to 1,824,393.
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