Competitions.csv contains data from competitions between antibiotic-resistant and sensitive bacteria against a marked strain (‘ara’). Genotypes are labelled by antibiotic resistance (‘CipR’: ciprofloxacin, ‘StrR’: streptomycin, ‘RifR’: rifampicin, ‘WT’: wild type), each competed against ara in the presence and absence of two phages. Six replicates (a-f) for each competition. ’N_0h’ and ’N_24h’ are total population sizes at the start and end in cfu/ml. ‘NA’ indicates no colonies detected. ‘ara_T4_Res’ gives the proportion of five ara colonies resistant to T4 at the end of the experiment; ‘comp_T4_Res’ gives the proportion of five colonies of the opposing genotype resistant to T4; ara_HK_Res and comp_HK_Res give the same against HK578. ‘mucoidy’ gives y or n depending on whether mucoid colonies were observed or not. ’s’ is calculated relative to the ancestral strain as described in the main text and online supplementary material. Metapopulations.csv contains data from experiments using the metapopulation approach described in Fig. S3. Columns are as above for Competitions.csv. Variable_frequency.csv contains data from experiments at variable starting ratios of RifR bacteria to ara, given under ‘Starting ratio’. Other columns are as above for Competitions.csv. Mutator_comps.csv contains data from 24h competitions between a mutS-deficient mutator genotype and ara. Columns are as above for Competitions.csv. Variable_MOI.csv contains data from 24h competitions between two resistant genotypes and ara in the presence or absence of phages at two different initial ratios of phage particles to bacterial cells (‘Phage_Bacteria_Ratio’, given approximately). Other columns are as above. 54_Generation_Comps.csv contains data from extended competitions between RifR genotypes (D516G and S512F), StrR genotypes (K43N and K88R), CipR genotypes (D87G and S83L), and the wild type against ara in the presence and absence of both phages, each replicated three times. ‘frequency’ at T0-T8 gives the frequency of the competing genotype relative to ara, estimated by plating on TA agar (at T1 from plating at a single dilution; at T2-T8 each culture was plated at several dilutions including undiluted culture). ‘OD’ gives population density estimated using a spectrophotometer as described in the main text and online supplementary material.