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A certain spectrum, indexed by a\in[0,\infty], of upper bounds P_a(X;x) onthe tail probability P(X\geq x), with P_0(X;x)=P(X\geq x) and P_\infty(X;x)being the best possible exponential upper bound on P(X\geq x), is shown to bestable and monotonic in a, x, and X, where x is a real number and X is a randomvariable. The bounds P_a(X;x) are optimal values in certain minimizationproblems. The corresponding spectrum, also indexed by a\in[0,\infty], of upperbounds Q_a(X;p) on the (1-p)-quantile of X is stable and monotonic in a, p, andX, with Q_0(X;p) equal the largest (1-p)-quantile of X. In certain sense, thequantile bounds Q_a(X;p) are usually close enough to the true quantilesQ_0(X;p). Moreover, Q_a(X;p) is subadditive in X if a\geq 1, as well aspositive-homogeneous and translation-invariant, and thus is a so-calledcoherent measure of risk. A number of other useful properties of the boundsP_a(X;x) and Q_a(X;p) are established. In particular, quite similarly to thebounds P_a(X;x) on the tail probabilities, the quantile bounds Q_a(X;p) are theoptimal values in certain minimization problems. This allows for acomparatively easy incorporation of the bounds P_a(X;x) and Q_a(X;p) into morespecialized optimization problems. It is shown that the minimization problemsfor which P_a(X;x) and Q_a(X;p) are the optimal values are in a certain sensedual to each other; in the case a=\infty this corresponds to the bilinearLegendre--Fenchel duality. In finance, the (1-p)-quantile Q_0(X;p) is known asthe value-at-risk (VaR), whereas the value of Q_1(X;p) is known as theconditional value-at-risk (CVaR) and also as the expected shortfall (ES),average value-at-risk (AVaR), and expected tail loss (ETL). It is shown thatthe quantile bounds Q_a(X;p) can be used as measures of economic inequality.The spectrum parameter, a, may be considered an index of sensitivity torisk/inequality.

An optimal three-way stable and monotonic spectrum of bounds on quantiles: a spectrum of coherent measures of financial risk and economic inequality