O. U. S. stands for the Oxford Union Society, the debating society of Oxford University that still exists today.

Their address is:

    The Oxford Union,
    Frewin Court,
    Oxford.
    OX1 3JB.

Their web site states that the society was founded in 1823 as a forum for discussion and debate, at a time when the free exchange of ideas was a notion foreign to the restrictive University authorities.  It soon became the only place for students to discuss political topics whilst at Oxford.  W.E. Gladstone, later to become one of the greatest British Prime Ministers, was one of the leading figures of the Union's early years.

Gladstone was President of the Union in 1830, shortly before entering the House of Commons.  Many others have followed him into politics and the Union can boast dozens of former members who have been active in its affairs whilst at Oxford and then gone on to become both nationally and internationally prominent figures.

For further details see the Oxford Union Society web site.

1858. Unofficial overprint type 45 in red.

a)  Vertical overprint, reading upwards

PP148 1d rose-red (SG 40 or C10)
Plates 27, 34, 36, 39, 41, 42, 43, 44, 46, 47, 48, 49, 52, 55, 56, 57, 58, 59, 60, 61, 62, 66 and 68

Used on cover
Plates 58 and 60 have been seen by the author.

PP148a 1d rose-red (SG 40 or C10) Overprint double

PP148b 1d rose-red (SG 40 or C10) Stop after S inverted (at top)
Plates ?

PP149 1d rose-red (SG 40 or C12)
Plate 50

PP150 1d rose-red (SG 40 or C13)
Plates R15 and R16

Used on cover
Plates R15 and R16

PP151 1d lake-red (SG 43 or G1)
Plates 71, 72, 73, 74, 76, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 121, 123, 125, 129, 130, 131, 132, 133, 134, 135, 137, 139, 140 and 142

PP151a 1d lake-red (SG 43 or G1) Overprint double
Plates 93, 95 and 112

PP151b 1d lake-red (SG 43 or G1) Watermark inverted
Plate 101

b)  Vertical overprint, reading downwards

PP152 1d rose-red (SG 40 or C10)
Plates 46, 47, 52 and 57

PP153 1d lake-red (SG 43 or G1)
Plates 95, 97 and 101

1869. Official underprint type 46 (under the gum) in red.

a)  Vertical underprint, reading upwards

PP154 1d lake-red (SG 43 or G1)
Plates 119, 124, 130, 134, 135, 136, 146, 150, 155, 156, 159, 160, 162, 163, 164, 165, 166, 169, 170, 171, 174, 177, 179, 182, 183, 185, 197, 199, 204, 205, 208, 212, 213, 215 and 218

PP154a 1d lake-red (SG 43 or G1) No stop after "O"
Plates ?

b)  Vertical underprint, reading downwards

PP155 1d lake-red (SG 43 or G1)
Plates 134, 143, 150, 156, 205, 212 and 213

PP155a 1d lake-red (SG 43 or G1) No stop after "O"
Plates ?

1880. Unofficial underprint type 45 (over the gum) in carmine.

a)  Vertical underprint, reading upwards

PP156 1d lake-red (SG 43 or G1)
Plates 199, 200 and 223

PP157 1d Venetian red (SG 166 or K3)

PP158 1d lilac, 14 dots (SG 171 or K7)

PP159 1d lilac, 16 dots (SG 173 or K8) Carmine underprint

PP160 1d lilac, 16 dots (SG 173 or K8) as PP159 but underprint in various other shades, brown-red to violet

b)  Vertical underprint, reading downwards

PP161 1d lake-red (SG 43 or G1)
Plates 199, 200, 202, 205, 208, 218, 221, 223 and 225

PP162 1d Venetian red (SG 166 or K3)

PP163 1d lilac, 14 dots (SG 171 or K7)

PP164 1d lilac, 16 dots (SG 173 or K8) Carmine underprint

PP165 1d lilac, 16 dots (SG 173 or K8) as PP159 but underprint in various other shades, brown-red to violet