A circumferential back-to-back seal assembly (1 or 21) with bifurcated flow comprising: (a) an annular seal housing (2 or 22) disposed between a pair of low pressure compartments (5, 6 or 58, 59), one said low pressure compartment (5 or 58) includes a gas, another said low pressure compartment (6 or 59) includes a lubricant; (b) a first annular seal ring (3 or 23); (c) a second annular seal ring (4 or 24), said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24) separately disposed within said annular seal housing (2 or 22), a high pressure gas communicable between said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24); (d) a rotatable runner (15 or 35), said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24) disposed around said rotatable runner (15 or 35); and (e) a plurality of groove structures (17, 37 or 41) disposed along an outer annular surface (16 or 36) of said rotatable runner (15 or 35), said high pressure gas communicable onto said groove structures (17, 37 or 41), each said groove structure (17, 37 or 41) separates said high pressure gas so that a first portion of said high pressure gas is directed onto said first annular seal ring (3 or 23) to form a first thin-film layer between said rotatable runner (15 or 35) and said first annular seal ring (3 or 23) and a second portion of said high pressure gas is directed onto said second annular seal ring (4 or 24) to form a second thin-film layer between said rotatable runner (15 or 35) and said second annular seal ring (4 or 24); characterized by, at least one of said plurality of groove structures (17, 37 or 41) is said groove structure which includes a pair of grooves disposed about and communicable with an annular groove along said outer annular surface (16 or 36) of said rotatable runner (15 or 35), said grooves disposed diagonally with respect to rotational direction of said rotatable runner (15 or 35). (a) an annular seal housing (2 or 22) disposed between a pair of low pressure compartments (5, 6 or 58, 59), one said low pressure compartment (5 or 58) includes a gas, another said low pressure compartment (6 or 59) includes a lubricant; (b) a first annular seal ring (3 or 23); (c) a second annular seal ring (4 or 24), said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24) separately disposed within said annular seal housing (2 or 22), a high pressure gas communicable between said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24); (d) a rotatable runner (15 or 35), said first annular seal ring (3 or 23) and said second annular seal ring (4 or 24) disposed around said rotatable runner (15 or 35); and (e) a plurality of groove structures (17, 37 or 41) disposed along an outer annular surface (16 or 36) of said rotatable runner (15 or 35), said high pressure gas communicable onto said groove structures (17, 37 or 41), each said groove structure (17, 37 or 41) separates said high pressure gas so that a first portion of said high pressure gas is directed onto said first annular seal ring (3 or 23) to form a first thin-film layer between said rotatable runner (15 or 35) and said first annular seal ring (3 or 23) and a second portion of said high pressure gas is directed onto said second annular seal ring (4 or 24) to form a second thin-film layer between said rotatable runner (15 or 35) and said second annular seal ring (4 or 24);