Inclusion Criteria:

          -  Considered to be eligible to receive platinum-based chemotherapy, in the
             investigator's judgment

          -  Documentation of recurrent/metastatic or locally advanced unresectable disease based
             on computed tomography (CT) or magnetic resonance imaging (MRI) scans

          -  Histologically or cytologically confirmed diagnosis of iCCA, eCCA, or GBC

          -  No prior systemic therapy for advanced BTC

          -  At least one measurable untreated lesion (per RECIST v1.1)

          -  Adequate biliary drainage with no evidence of ongoing infection

          -  Eastern Cooperative Oncology Group Performance Status of 0 or 1

          -  Life expectancy of > 3 months

          -  Adequate hematologic and end-organ function

          -  For women of childbearing potential: agreement to remain abstinent (refrain from
             heterosexual intercourse) or use contraceptive methods, and agreement to refrain from
             donating eggs

          -  For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use
             a condom, and agreement to refrain from donating sperm

        Exclusion Criteria:

          -  Recurrent disease <=6 months after curative surgery or <= 6 months after the
             completion of adjuvant therapy

          -  Prior local regional therapy such as radioembolization

          -  Combined or mixed hepatocellular/cholangiocarcinoma

          -  Clinically significant hepatic encephalopathy within the 12 months prior to Day 1 of
             Cycle 1

          -  National Cancer Institute Common Terminoogy Criteria for Adverse Events Grade >= 2
             peripheral neuropathy

          -  Prior bleeding event due to untreated or incompletely treated esophageal and/or
             gastric varices within 6 months prior to Day 1 of Cycle 1

          -  Pregnant or breastfeeding, or intending to become pregnant during the study or within
             5 months after the final dose of atezolizumab or within 6 months after the final dose
             of bevacizumab, cisplatin or gemcitabine

          -  Active or history of autoimmune disease or immune deficiency

          -  History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced
             pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening
             chest computed tomography scan

          -  History of malignancy other than BTC within 5 years prior to screening, with the
             exception of malignancies with a negligible risk of metastasis or death

          -  Symptomatic, untreated, or actively progressing CNS metastases

          -  For patients with lung metastases, if one of the following criteria applies: Large,
             centrally located pulmonary metastases; Clear tumor infiltration into the thoracic
             great vessels seen on imaging; Clear cavitation of pulmonary lesions seen on imaging

          -  Active tuberculosis

          -  Co-infection with HBV and HCV

          -  Treatment with systemic immunostimulatory agents or immunosuppressive medication

          -  Inadequately controlled arterial hypertension

          -  History of hypertensive crisis or hypertensive encephalopathy

          -  Significant vascular disease

          -  Evidence of bleeding diathesis or significant coagulopathy

          -  Serious, non-healing or dehiscing wound, active ulcer, or untreated bone fracture

          -  Chronic daily treatment with a non-steroidal anti-inflammatory drug (NSAID)

          -  Preexisting renal impairment, myelosuppression, or hearing impairment