** Jefferies updates ratings on oil cos, seeing value in thebeaten-down sector
** Tullow Oil up 3.1 pct, second-largest large-capgainer in Europe as Jefferies upgrades rating to "hold"
** Analysts upgrade stock, which is down 49 pct YTD, as itnow trades near Jefferies' revised PT of 191p (its Thursdayclose was 192.4p)
** Jefferies cut PT on Premier Oil -- to 116p from180p -- but reiterate "buy"; shares in co up 1.2 pct
** Tullow, Premier also recovering from Thursday falls,which trader calls overdone
** Ophir down 1.1 pct as Jefferies cuts to "hold"from "buy"
** BP, Cairn, BG up 0.1-0.7 pct
** Energy sector one of two in positive territory on theFTSE 350 Index (venkateshasoumithri.mamidipudi.thomsonreuters.com@reuters.net)