Rubidium and caesium must be kept away from air, even under oil, because even a small amount of air diffused into the oil may trigger formation of the dangerously explosive peroxide; for the same reason, potassium should not be stored under oil in an oxygen-containing atmosphere for longer than 6 months.
ɹuːbˈɪdiəm ænd sˈiːsiəm mˈʌst biː kˈɛpt ɐwˈeɪ fɹʌm ˈɛɹ, ˈiːvən ˌʌndɚɹ ˈɔɪl, bɪkˈʌz ˈiːvən ɐ smˈɔːl ɐmˈaʊnt ʌv ˈɛɹ dᵻfjˈuːzd ˌɪntʊ ðɪ ˈɔɪl mˈeɪ tɹˈɪɡɚ fɔːɹmˈeɪʃən ʌvðə dˈeɪndʒɚɹəsli ɛksplˈoʊsɪv pəɹˈɑːksaɪd; fɚðə sˈeɪm ɹˈiːzən, pətˈæsiəm ʃˌʊd nˌɑːt biː stˈoːɹd ˌʌndɚɹ ˈɔɪl ɪn ɐn ˈɑːksɪdʒəŋkəntˈeɪnɪŋ ˈætməsfˌɪɹ fɔːɹ lˈɔŋɡɚ ðɐn sˈɪks mˈʌnθs.